How can I effectively play a dominant 9th chord on the piano?

To play a dominant 9th chord on the piano, start with the root note of the chord, then add the major 3rd, perfect 5th, minor 7th, and major 9th notes. Play all these notes together to create the full dominant 9th chord. Practice playing this chord shape in different inversions and experiment with different voicings to find the sound you like best.