I want to send coap messages using an application developed on nativescript framework. Are there any available modules in nativescript or how to use node-coap for the same?
I don't think there is any plugin as of today that supports CoAP. You might want to write one.
A quick search shows there are native clients available on respective platforms, iCoAP / spitfirefox for which you could write a plugin or directly use the apis in your project.
Read more about accessing native or third party libraries in iOS / Android from the docs.