Thank you for contacting us on this.
Currently, you can create new triggers directly from The Welkin Suite for your regular Salesforce projects, and we are going to implement this ability for SFDX projects in one of the nearest versions of TWS.
At the same time, right now you can use the built-in command line in TWS to create a new trigger file in your Salesforce DX project. (Here is a command for a trigger creation)
I will keep you updated when we will implement a trigger creation for SFDX.
If you would have any other questions or suggestions, please let us know - we'll be happy to assist.