1. Bend your knees and bend your body at a 45 degree angle.
(Does this sentence mean 'bend your knee at 45 degree angle or not'?)
2. Bend your knees and bend your body at a 45-degree angle.
(Is this correct? There is a hyphen between 45 and degree.)
Neither sentence makes sense to me. I don't know how a person can bend his/her knees into a 45-degree angle AND THEN bend his/her body into a 45-degree angle. It sounds impossible to me!
Yes. the hyphen is needed. Didn't I give you this link before?
See "a" in the examples/explanation list.posted by Writeacher