Pick out the key for the pentatonic scale type in “backing track in key of A for guitar” for example and see what comes up. You will find several different options based on the type of jam you want to play and the speed of the beat. Check out a couple different tracks and start jamming on your pentatonic scales while incorporating some riffs, licks and bends and listen to the tone and pitch. If you can tune your guitar with a pitch pipe you should be able to hear the notes that are in or out of key.
When you are doing your bends in the pentatonic scales you have to be especially aware of the pitch of the bend. The bluesy sound of the blues comes in part from the bending of the strings to add emphasis and feeling. However, bending of the guitar strings will change the pitch of that note and it can bring the note into or out of the proper key. The only way to keep the pitch of the note in the right key when bending notes in the pentatonic scale is by ear and therefore by many hours of practice with backing tracks.
Pentatonic Scales: Playing Guitar Pentatonic Scales with Backing Tracks