I had left side inguinal hernia repair (incision/mesh) 9 weeks ago. Numbness in groin is fading, but I now have burning in testicle/incision area. Why?

Healing process . Probably relate to the the healing process. Doesn't sound dangerous. If it persists and limits your activity, or gets worse, see your surgeon again. If no answers, consider a second opinion from a general surgeon with experience in hernia repair. Check the americas hernia society website to find surgeons that are members. Whole this is no guarantee of quality, it demonstrates some interest.
Go for follow up. With your surgeon, will check you , as part of healing process , in couple of wks you will be fine.