If I need to incorporate dat.gui in my project, which line I must add to my html?
This doesn’t seem to work. Is there a full web address for dat.gui.js?
I am not sure whether Dat.gui is still supported or not, but, why Dat.gui and not Babylon GUI?
Yep, that’s what I’m doing at the moment 
You can find and copy the code for dat.gui.js from here
Or use npm
$ npm install --save dat.gui