Any more details on what you're trying to do?
Knife tool seems to work the same in my X6 as it did in X3, although generally I prefer to powerclip things if I'm breaking it up into multiple objects for printing, if just doing cut only for vinyl, then usually I'll just use the shape tools.
If you're trying to work on a group of objects, I don't think the knife will work, if you combine the objects, you will generally only cut one path, and not sever the entirety (which is why I usually prefer to powerclip).
Knife tool seems to work the same in my X6 as it did in X3, although generally I prefer to powerclip things if I'm breaking it up into multiple objects for printing, if just doing cut only for vinyl, then usually I'll just use the shape tools.
If you're trying to work on a group of objects, I don't think the knife will work, if you combine the objects, you will generally only cut one path, and not sever the entirety (which is why I usually prefer to powerclip).