Dark purple spot on front of knee with tiny hard bump under it. did not hit it and it isn't a bite. is it a sign of a dvt?

Unlikely: The deep veins do not run in the area you describe. Purple is frequently a bruise-? Any other illnesses or bruising tendency? Commonly we forget a minor trauma?

Purple spot on knee.: What you describe may be trapped blood or an area of superficial phlebitis. It is hard to say what it is without a picture. This is not a sign of DVT. You should see a dermatologist or a vein specialist for an evaluation.