Which type of frame for slopestyle? So I'm looking to build a slopestyle-trail kind of bikes, something like Brandon Semenuk used in Redbull Raw videos. I want something I can use on trails while being playful enough to commute on the street (and jumping on stuff). But I don't know which frame to start with.

Can I use trail frame like Stumpjumper FSR or do I need a purpose built slopestyle? what is the difference in geometry (if any)?
There is no perfect all-rounder. Slopestyle bikes are basically dirt jump bikes with the suspension designed to soak the harshest of impacts. This suspension design was never thought to behave like a normal bike suspesnsion, that used to "even rough trails". Typically slopestyle riders put a lot of pressure in their air shocks to prevent bottoming out.

Now, I'm not sure what do you mean by "something I can use on trails while being playful enough to commute on the street (and jumping on stuff)". Do you have some dirt jumps or nice skateparks around you, so you could use your DJ bike to its full potential? Or maybe you want to ride most of the time your local MTB trails and add some manuals and bunnyhops here and there? You should be honest with yourself, no normal trail bike will be suitable for average dirt jumping (it will be practically impossible to do a barspin or a tailwhip, and plush suspension will swallow all pumping rhythm), as no 100% DJ/slopestyle will be suitable for a fun round on normal MTB trail (imagine doing off-camber turn with an almost rigid bike, or pedaling 30 km + with a frame sized two sizes below your regular). Either choose one, or both.

To summarize, I would recommend you learn to manual and bunnyhop on your SJ, then pay a visit to local DJ / skatepark and try to get some airtime and learn some basic DJ tricks (whips, tables). If you'll have the feeling it's fun then go ahead and buy a DJ bike. Otherwise, save your money for something else.

EDIT: looks like GMBN heard your voice and did a video on riding a slopestyle bike in a bike park. Check it, it's quite entertaining. I guess this won't leave you any doubts about slopestyle bike specialization. Click