If you want to know the note names of the played pitches, then tap the home button and choose "Preferences". There you can turn on "Display Pitch Names". Also, the name of the row in the middle of the screen is also the name of the key you're currently playing. The first time you'll start SoundPrism it will be set to the key of C major.
To change the key in SoundPrism tap the up or the down button. The whole pitch system is moved and note names of the new key are shown.
The note name in the middle indicates the key you're currently playing in. In the picture it is C major.
The video of an older version of SoundPrism demonstrates how to play melodies on SoundPrism and how to move them around different notes and keys as a pattern.