Scales to Play Over Bm(add9)
Every chord is a subset of several scales: any scale that contains all of a chord's tones fits over it. Pick a chord to see the matching scales from its own root, the major keys the chord belongs to, and full fretboard diagrams for every scale on guitar.
A Bm(add9) chord contains the notes B – C# – D – F#. Any scale that includes every one of those 4 tones fits over it — from the root B, that means B Natural Minor, B Melodic Minor, B Harmonic Minor, B Rock 'n' Roll, B Dorian, B Dorian Bebop and B Gypsy Minor. Start with the first scale listed: it is the most common choice, and the others color the same chord tones differently.
Bm(add9) is also diatonic to 2 major keys: A major (relative minor F#m), D major (relative minor Bm). In a song from one of those keys you can also solo with the key's own major scale or its relative minor pentatonic across the whole progression, not just this chord.