Watch the 1 5 1 Structures online guitar lesson by Brad Carlton from Guitar Lab: Open String Universe
This chord is A root 5th root structure rooted off the 5th fret of the 5th string. The 2nd string open is a B which is the 6 in the key of D. The 1st string open is an E which is the 9(2) in the key of D. The total formula of this voicing is 1 2 5 6 therefore it is a D 6/9 (no 3). The formula 1 2 5 6 is a subset of the following scales: ionian, dorian, lydian, mixolydian, melodic minor, overtone. The included chart shows this chord/scale relationship for the 6/9 (no 3) harmony.