Scales to Play Over Bm7b5
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 Bm7b5 chord contains the notes B – D – F – A. Any scale that includes every one of those 4 tones fits over it — from the root B, that means B Blues, B Locrian, B Half Whole Diminished and B Gypsy Major. Start with the first scale listed: it is the most common choice, and the others color the same chord tones differently.
Bm7b5 is also diatonic to one major key: C major (relative minor Am). 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.