Guitar chords in the key of G:
G Am Bm C D Em F#dim

Chord G7-5 notes: G, Db, F, B and B. You should not play the 1st string.

The string 2 (B) is left open.

G dominant 7th flat 5th guitar chord's alternative names: G7b5, Gdom7b5.

Steps: 1-3-b5-b7.
1(G), 3(B), b5(C#/Db), b7(F).