how can i trigger a button for print message in verse ?
Can you please clarify what you are wanting to do? Are you trying to print a message when a button is pressed?
yes
I would like the answer to this as well 
As part of our documentation there is a page which describes how to respond to a button event here Coding Device Interactions
but how do you assign Button and object that will spawn to the instance ?
it feels that part is missing
In Coding Device Interactions it walks through an example of handling this interaction in a Verse script. To print a message to the screen you would add a popup_dialog_device to your scene and script and then call my_popup_dialog.Show() in the OnButtonInteractedWith function used in the provided example.
For you follow-up question, once you add a button device to your world, it will show up in the Button dropdown so you can select it.
