Here are a list of libcoap API individual man pages, some of which have code examples:

coap_add_attr(3)
coap_add_data(3)
coap_add_data_blocked_response(3)
coap_add_data_large_request(3)
coap_add_data_large_response(3)
coap_add_option(3)
coap_add_optlist_pdu(3)
coap_add_resource(3)
coap_add_token(3)
coap_addr_info_t(3)
coap_address_copy(3)
coap_address_equals(3)
coap_address_get_port(3)
coap_address_init(3)
coap_address_set_port(3)
coap_address_set_unix_domain(3)
coap_address_t(3)
coap_af_unix_is_supported(3)
coap_async_get_app_data(3)
coap_async_is_supported(3)
coap_async_set_app_data(3)
coap_async_set_delay(3)
coap_async_trigger(3)
coap_attr_get_value(3)
coap_binary_equal(3)
coap_block_build_body(3)
coap_cache_derive_key(3)
coap_cache_derive_key_w_ignore(3)
coap_cache_get_app_data(3)
coap_cache_get_by_key(3)
coap_cache_get_by_pdu(3)
coap_cache_get_pdu(3)
coap_cache_ignore_options(3)
coap_cache_set_app_data(3)
coap_can_exit(3)
coap_cancel_observe(3)
coap_check_option(3)
coap_cleanup(3)
coap_clear_event_handler(3)
coap_client_is_supported(3)
coap_clone_uri(3)
coap_context_get_app_data(3)
coap_context_get_coap_fd(3)
coap_context_get_csm_timeout(3)
coap_context_get_csm_timeout_ms(3)
coap_context_get_max_handshake_sessions(3)
coap_context_get_max_idle_sessions(3)
coap_context_get_session_timeout(3)
coap_context_oscore_server(3)
coap_context_set_app_data(3)
coap_context_set_block_mode(3)
coap_context_set_cid_tuple_change(3)
coap_context_set_csm_timeout(3)
coap_context_set_csm_timeout_ms(3)
coap_context_set_keepalive(3)
coap_context_set_max_block_size(3)
coap_context_set_max_handshake_sessions(3)
coap_context_set_max_idle_sessions(3)
coap_context_set_max_token_size(3)
coap_context_set_pki(3)
coap_context_set_pki_root_cas(3)
coap_context_set_psk(3)
coap_context_set_psk2(3)
coap_context_set_session_timeout(3)
coap_debug_set_packet_loss(3)
coap_decode_var_bytes(3)
coap_decode_var_bytes8(3)
coap_delete_bin_const(3)
coap_delete_binary(3)
coap_delete_cache_entry(3)
coap_delete_cache_key(3)
coap_delete_optlist(3)
coap_delete_oscore_conf(3)
coap_delete_oscore_recipient(3)
coap_delete_pdu(3)
coap_delete_resource(3)
coap_delete_str_const(3)
coap_delete_string(3)
coap_delete_uri(3)
coap_dtls_cid_is_supported(3)
coap_dtls_cpsk_t(3)
coap_dtls_get_log_level(3)
coap_dtls_is_supported(3)
coap_dtls_log(3)
coap_dtls_pkcs11_is_supported(3)
coap_dtls_pki_is_supported(3)
coap_dtls_pki_t(3)
coap_dtls_psk_is_supported(3)
coap_dtls_rpk_is_supported(3)
coap_dtls_set_log_level(3)
coap_dtls_spsk_t(3)
coap_enable_pdu_data_output(3)
coap_encode_var_bytes(3)
coap_encode_var_safe(3)
coap_encode_var_safe8(3)
coap_endpoint_set_default_mtu(3)
coap_endpoint_str(3)
coap_epoll_is_supported(3)
coap_find_async(3)
coap_find_attr(3)
coap_free_address_info(3)
coap_free_async(3)
coap_free_context(3)
coap_free_endpoint(3)
coap_get_app_data(3)
coap_get_available_scheme_hint_bits(3)
coap_get_data(3)
coap_get_data_large(3)
coap_get_log_level(3)
coap_get_resource_from_uri_path(3)
coap_get_tls_library_version(3)
coap_get_uri_path(3)
coap_host_is_unix_domain(3)
coap_insert_optlist(3)
coap_io_do_epoll(3)
coap_io_do_io(3)
coap_io_pending(3)
coap_io_prepare_epoll(3)
coap_io_prepare_io(3)
coap_io_process(3)
coap_io_process_with_fds(3)
coap_ipv4_is_supported(3)
coap_ipv6_is_supported(3)
coap_is_af_unix(3)
coap_is_bcast(3)
coap_is_mcast(3)
coap_join_mcast_group_intf(3)
coap_lock_callback(3)
coap_lock_callback_release(3)
coap_lock_callback_ret(3)
coap_lock_callback_ret_release(3)
coap_lock_check_locked(3)
coap_lock_init(3)
coap_lock_invert(3)
coap_lock_lock(3)
coap_lock_unlock(3)
coap_log(3)
coap_log_alert(3)
coap_log_crit(3)
coap_log_debug(3)
coap_log_emerg(3)
coap_log_err(3)
coap_log_info(3)
coap_log_level_desc(3)
coap_log_notice(3)
coap_log_oscore(3)
coap_log_warn(3)
coap_lwip_dump_memory_pools(3)
coap_lwip_set_input_wait_handler(3)
coap_make_str_const(3)
coap_mcast_per_resource(3)
coap_mcast_set_hops(3)
coap_new_bin_const(3)
coap_new_binary(3)
coap_new_cache_entry(3)
coap_new_client_session(3)
coap_new_client_session_oscore(3)
coap_new_client_session_oscore_pki(3)
coap_new_client_session_oscore_psk(3)
coap_new_client_session_pki(3)
coap_new_client_session_psk(3)
coap_new_client_session_psk2(3)
coap_new_context(3)
coap_new_endpoint(3)
coap_new_message_id(3)
coap_new_optlist(3)
coap_new_oscore_conf(3)
coap_new_oscore_recipient(3)
coap_new_pdu(3)
coap_new_str_const(3)
coap_new_string(3)
coap_new_uri(3)
coap_observe_persist_is_supported(3)
coap_opt_length(3)
coap_opt_value(3)
coap_option_clrb(3)
coap_option_filter_clear(3)
coap_option_filter_get(3)
coap_option_filter_set(3)
coap_option_filter_unset(3)
coap_option_getb(3)
coap_option_iterator_init(3)
coap_option_next(3)
coap_option_setb(3)
coap_oscore_is_supported(3)
coap_package_build(3)
coap_package_name(3)
coap_package_version(3)
coap_path_into_optlist(3)
coap_pdu_get_code(3)
coap_pdu_get_mid(3)
coap_pdu_get_token(3)
coap_pdu_get_type(3)
coap_pdu_init(3)
coap_pdu_set_code(3)
coap_pdu_set_mid(3)
coap_pdu_set_type(3)
coap_persist_observe_add(3)
coap_persist_set_observe_num(3)
coap_persist_startup(3)
coap_persist_stop(3)
coap_persist_track_funcs(3)
coap_print_addr(3)
coap_print_ip_addr(3)
coap_print_wellknown(3)
coap_proxy_forward_request(3)
coap_proxy_forward_response(3)
coap_proxy_is_supported(3)
coap_q_block_is_supported(3)
coap_query_into_optlist(3)
coap_read(3)
coap_register_async(3)
coap_register_event_handler(3)
coap_register_handler(3)
coap_register_nack_handler(3)
coap_register_ping_handler(3)
coap_register_pong_handler(3)
coap_register_request_handler(3)
coap_register_response_handler(3)
coap_resize_binary(3)
coap_resolve_address_info(3)
coap_resource_get_uri_path(3)
coap_resource_get_userdata(3)
coap_resource_init(3)
coap_resource_notify_observers(3)
coap_resource_proxy_uri_init(3)
coap_resource_proxy_uri_init2(3)
coap_resource_release_userdata_handler(3)
coap_resource_reverse_proxy_init(3)
coap_resource_set_dirty(3)
coap_resource_set_get_observable(3)
coap_resource_set_mode(3)
coap_resource_set_userdata(3)
coap_resource_unknown_init(3)
coap_resource_unknown_init2(3)
coap_run_once(3)
coap_send(3)
coap_send_recv(3)
coap_send_recv_terminate(3)
coap_server_is_supported(3)
coap_session_disconnected(3)
coap_session_get_ack_random_factor(3)
coap_session_get_ack_timeout(3)
coap_session_get_addr_local(3)
coap_session_get_addr_mcast(3)
coap_session_get_addr_remote(3)
coap_session_get_app_data(3)
coap_session_get_context(3)
coap_session_get_default_leisure(3)
coap_session_get_ifindex(3)
coap_session_get_max_payloads(3)
coap_session_get_max_retransmit(3)
coap_session_get_non_max_retransmit(3)
coap_session_get_non_receive_timeout(3)
coap_session_get_non_timeout(3)
coap_session_get_nstart(3)
coap_session_get_probing_rate(3)
coap_session_get_proto(3)
coap_session_get_psk_hint(3)
coap_session_get_psk_key(3)
coap_session_get_state(3)
coap_session_get_tls(3)
coap_session_get_type(3)
coap_session_init_token(3)
coap_session_max_pdu_size(3)
coap_session_new_token(3)
coap_session_reference(3)
coap_session_release(3)
coap_session_set_ack_random_factor(3)
coap_session_set_ack_timeout(3)
coap_session_set_app_data(3)
coap_session_set_default_leisure(3)
coap_session_set_max_payloads(3)
coap_session_set_max_retransmit(3)
coap_session_set_mtu(3)
coap_session_set_no_observe_cancel(3)
coap_session_set_non_max_retransmit(3)
coap_session_set_non_receive_timeout(3)
coap_session_set_non_timeout(3)
coap_session_set_nstart(3)
coap_session_set_probing_rate(3)
coap_session_set_type_client(3)
coap_session_str(3)
coap_set_app_data(3)
coap_set_event_handler(3)
coap_set_log_handler(3)
coap_set_log_level(3)
coap_set_show_pdu_output(3)
coap_show_pdu(3)
coap_show_tls_version(3)
coap_sockaddr_un(3)
coap_split_path(3)
coap_split_proxy_uri(3)
coap_split_query(3)
coap_split_uri(3)
coap_startup(3)
coap_string_equal(3)
coap_string_tls_support(3)
coap_string_tls_version(3)
coap_tcp_is_supported(3)
coap_threadsafe_is_supported(3)
coap_tls_engine_configure(3)
coap_tls_engine_remove(3)
coap_tls_is_supported(3)
coap_uri_into_options(3)
coap_uri_into_optlist(3)
coap_verify_proxy_scheme_supported(3)
coap_write(3)
coap_ws_is_supported(3)
coap_ws_set_host_request(3)
coap_wss_is_supported(3)