Smeargle gets the special move Sketch, which allows him to copy any mover permanently. I plan on "sketching" out some plans for Smeargles (see what I did there), and I want to know which moves are a no-go, if any.
Simply anything but Chatter and Struggle as Bulbapedia states. You also can't Sketch Sketch I think. Struggle isn't really intended to be a "move", and Chatter is a Chatot exclusive, and highly unusual, move.
Chatter is the one of only three moves that cannot be Sketched, presumably because as a field move, if used by a Pokémon other than Chatot, it does not temporarily change the battle cry of the respective Pokémon to the recorded version even if audio is recorded. This is because recording audio via Chatter activates a Pokémon's alternative cry, where Chatot's alternative cry exclusively depends on what was recorded when the Chatter field move is used; however, Chatter still remains not Sketchable even in Generation VI, where vocals cannot be recorded.
well from doing field research with my trainer I can sketch any move except Struggle. chatter I don't know yet since he has yet to get a Chatot. but I am able to Sketch Transform (though it takes a bit of practice for timing on use.) I also Sketched both Baneful Bunker (Toxapex exclusive move) and Happy Hour (Munchlax exclusive move). so the pokemon Exclusive rule does not apply to Sketch.