Mario Hoops 3 on 3

You need to be close to the hoop, first. Stroke the stylus up and the character will automatically dunk. Stroke up twice and then rub the stylus around to get coins, then stroke down to dunk. Stroke up twice and down once quickly to do a "quick dunk."

Do you mean the special shots? If so, you tap it out, not trace. It can be a bit annoying, though.

You stroke up from any angle and hope you make it. Also you can get close to the hoop and stroke up. For special shot you need to do practice where it says special shots. For the other special shot you shot hold your stylus on the screen and then stroke up to make it in the hoop. You can also get close to the hoop and stroke up twice and then rub the stylus around to get coins. Lastly, you can stroke up twice and down once quickly to do a quick dunk. That is pretty much it.

To do a dunk, run up to the basket and do one of the following actions depending on what control type you're using:
1. If you're using the buttons, press X (or Up if you set it to left-handed). Double tap it to do a quick dunk or press it twice and hold it on the second press to gain rings and then dunk.
2. If you're using the stylus, stroke up. Stroke up and down quickly to do a quick dunk. Stroke up twice and move the stylus back and forth from left to right to gain rings and stroke down to dunk.
Special shots/dunks are the ones that require tapping out the character formations. If you tap out the formation twice without getting hurt, you'll do the special shot. If you're outside the 3-point line, you'll do an alley-oop (a pass to a player in the air for a dunk). If you're inside the 3-point line, you'll do the special shot on your own.
Hope this helps!