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_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_cancel_observe(3)
coap_check_option(3)
coap_context_get_coap_fd(3)
coap_context_get_csm_timeout(3)
coap_context_get_max_handshake_sessions(3)
coap_context_get_max_idle_sessions(3)
coap_context_get_session_timeout(3)
coap_context_set_block_mode(3)
coap_context_set_csm_timeout(3)
coap_context_set_keepalive(3)
coap_context_set_max_handshake_sessions(3)
coap_context_set_max_idle_sessions(3)
coap_context_set_pki(3)
coap_context_set_pki_root_cas(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_binary(3)
coap_delete_bin_const(3)
coap_delete_cache_entry(3)
coap_delete_cache_key(3)
coap_delete_optlist(3)
coap_delete_resource(3)
coap_delete_str_const(3)
coap_delete_string(3)
coap_dtls_cpsk_t(3)
coap_dtls_is_supported(3)
coap_dtls_pki_t(3)
coap_dtls_spsk_t(3)
coap_encode_var_safe(3)
coap_encode_var_safe8(3)
coap_endpoint_set_default_mtu(3)
coap_endpoint_str(3)
coap_find_async(3)
coap_find_attr(3)
coap_free_async(3)
coap_free_context(3)
coap_free_endpoint(3)
coap_get_data(3)
coap_get_data_large(3)
coap_get_log_level(3)
coap_get_tls_library_version(3)
coap_get_uri_path(3)
coap_insert_optlist(3)
coap_io_can_exit(3)
coap_io_do_epoll(3)
coap_io_do_io(3)
coap_io_prepare_epoll(3)
coap_io_prepare_io(3)
coap_io_process(3)
coap_io_process_with_fds(3)
coap_join_mcast_group_intf(3)
coap_log(3)
coap_make_str_const(3)
coap_mcast_per_resource(3)
coap_new_binary(3)
coap_new_bin_const(3)
coap_new_cache_entry(3)
coap_new_client_session(3)
coap_new_client_session_pki(3)
coap_new_client_session_psk2(3)
coap_new_context(3)
coap_new_endpoint(3)
coap_new_optlist(3)
coap_new_pdu(3)
coap_new_str_const(3)
coap_new_string(3)
coap_option_filter_clear(3)
coap_option_filter_get(3)
coap_option_filter_set(3)
coap_option_filter_unset(3)
coap_option_iterator_init(3)
coap_option_next(3)
coap_opt_length(3)
coap_opt_value(3)
coap_package_build(3)
coap_package_name(3)
coap_package_version(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_register_async(3)
coap_register_event_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_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_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_send(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_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_retransmit(3)
coap_session_get_nstart(3)
coap_session_get_probing_wait(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_retransmit(3)
coap_session_set_mtu(3)
coap_session_set_no_observe_cancel(3)
coap_session_set_nstart(3)
coap_session_set_probing_wait(3)
coap_session_set_type_client(3)
coap_session_str(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_split_path(3)
coap_split_query(3)
coap_string_equal(3)
coap_string_tls_support(3)
coap_string_tls_version(3)
coap_tcp_is_supported(3)
coap_tls_is_supported(3)