His down smash is really freaking hard to WD OOS > punish on. So I don't really recommend going for a direct punish on it. Instead, I'd suggest just WDing into a decent range for Sheik's generic attack spacing and then going from there. Sheik wins mainly by just doing what Doc does in the MU but she's better at it so just try to play to that.
F-tilt is really dangerous when he's on the ground. He's gonna try to run into it and crouch into a good counterattack, or shield into an up smash OOS or grab (up smash works if you're not tipping it, basically). Doc depends kind of heavily on people attacking him with weak moves and him netting a good counterattack from it, so just grab him and do a generic throw combo. Not much really works on him, but as long as you keep him from getting his footing back you can do some long fake combos that rack reasonable damage. I actually do recommend f-tilt after d-throw vs DI away on this guy sometimes because the regrab is really hard and it's easier to just keep him in the air anyway.
Doc likes to full jump and try to out-time Sheik's tilts and slap and then come in with stuff. You can counter this by just running by him and bairing though. Bair in general is really good against him, same with fair. Dash dance into grab or dash attack is also pretty good vs his ground game.
Don't fall for the tornado recovery. Bair through pills or around them. Manage your invulnerability well.
Good luck!
