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.

An FUE is treated just like a regular hair transplant with regard to the recipient area, but the donor area has open wounds which require daily washing with soap and water. Within 3 days of surgery, you can resume full activities, heavy exercises if you wish. The recipient area requires daily washes as well to keep the recipient area free of crusts. I generally recommend the use of a sponge and supply my patient with a surgical sponge to fill with soapy water and press on the recipient area daily. By repeating this daily, all crusts can be washed off without any fear of losing grafts. IF any crust are present, use a Q tip and dip it into soapy water, and roll it on the crusts and that will lift them off without dislodging them, but never rub them, just roll the Q tip on the recipient crust. I like to see no evidence of any crusting in the recipient area and the crusts from the donor area gone in 7-10 days with daily washing.