When can I wash off scabs I'm 11 days post FUE surgery? What's the safest way?

At 11 days, you should be able to wash your head. It is good practice to keep the area moist with for example bacitracin ointment if you have stubborn scabs. This serves the purpose of loosening up the scabs over a few days rendering them easier to come off with less efforts

The safest way to take care of your scalp  and scabs after surgery is to follow the instructions given by your doctor.  If you are concerned it would be better to go back to your doctor so your doctor can wash your hair for you.

After about a week it's safe to gently massage the scabs off while you're showering. After rubbing in shampoo, let it sit for 5+ minutes before rinsing. Then gently rub in conditioner and let it sit for 5+ minutes as well. But before rinsing out the conditioner, you can use your finger pads to slowly rub the scabs, which should loosen them so they fall off. If that isn't enough and you still feel like you're pulling them, try rubbing in baby oil and letting that soak before again trying to rub the scabs off.
As always, if you have concerns it is best to ask your doctor, who knows the details specific to your case.