The short answer is find out what key signature you're in. You should be able to determine that from either sheet music or taking note of what the accidentals are. Let's say you're in the key of Eb. The major scale would Eb, F, G, Ab, Bb, C, and D. The chords in the key of Eb are Eb, Fm, Gm, Ab, Bb, Cdim. The notes of the triads for each chord will be your targets for chord changes.
It'll be easier to stay with the same chord and do your solo, not worrying to much about the target notes. You would use one scale in a key, hitting target notes when the chord changes but those notes will be in the scale.