Overall, right around 40% (somewhere in the 38-44% range). I'm hoping for 35% or so from three. He improved his long ball a lot last year, and I expect that to continue improving.
As others have said though, looking at raw FG % is a very poor way to asses someone's offensive game. DeAndre Jordan led the league in FG % last year, but if you told him he couldn't dunk he might never score again.
Even with what I hope is additional minutes as the primary ball-handler, Smart will probably still be taking a whole bunch of bail-out 3s at the end of broken possessions again, at least this year, and that will keep his raw FG% down. What I really want to see is Smart generating FTA's. If he can get his 3pt shot up to around 36% in the future (seems almost certain at this point), and he's able to get to the line a lot, that could be the difference between him being a solid starter or an All-Star. A guy like Thomas can generate 20 points on his coldest shooting day just by getting FTA's. If Smart can do that, he could be really special.