DP8

This app is very accessible, but the buttons are not all labeled correctly. Here's the list of buttons and their assigned functions.
NOTE: To play the drum kit you must disable VoiceOver.

PROPADLOUD / PROPADDYN: This changes whether different parts of a drum piece play at a different volume or not. For example, hitting the snare at the bottom will play very quietly, and hitting the snare at the top will slam it. You can double-tap this button to change it, sort of like a toggle.
crBdSync / crBdUnsync: this button changes whether the kick synchronizes with the cymbal or not. @If it is set to sync, the kick will play with the cymbal. If it's set to unsync the cymbal will be the only thing that plays.
stylePOP / Rock / Jazz: This button toggles between the different drum kits.
mediaLibrary: Opens your music library to jam along with your favorite tunes.
rewind btn: Rewind function
play btn: play function
songVol / speed / sysVol:Th is a toggle button that toggles to different volume adjustments. The slider to the right of the toggle will control whatever the toggle is set to. For example, if I toggled it to songSpeed, the slider to the right would adjust the speed of the song playing at that moment.
Here's the list of pads on the screen with VoiceOver off.
Kick: bottom left
Snare: Bottom middle.
Rimshot (if kit supports it): below snare
Floor tom: bottom half right
HiHat open / closed: bottom right
Toms: middle of the screen, from middle left to almost middle right.
Cymbal: top left
Ride: top right. Cowbell is somewhere above it.

Hope this helps!