To play the D7 chord, perform a barre by pressing your index finger on the top g-string, C-string, and E-string on the 2nd fret and middle finger on the 3rd fret of the bottom A-string.
D7 Ukulele Chord Explanation
The D7 chord contains the notes D-F#-A-C.
To build a D7 chord, take the dominant seventh formula (1-3-5-b7) and apply it to the D major scale (D, E, F#, G, A, B, C#).
Identify the first, third, fifth, and flat seventh scale degrees in the D major scale which are D-F#-A-C.
Notice how the seventh scale degree found in the chord is lowered a half step as indicated by the "flat" or "b" that precedes the number "b7". In this case, the seventh scale degree of a D major scale – a "C#" note is lowered a half step to a "C" note to make the chord a dominant seventh chord.
Watch the following video to learn how to play a D7 chord on ukulele.