If you have hair loss due to chemical "damage". There is no "method" to find out if you have "roots" still left in the area. The best method is to wait. If there are "roots" it will take several months for the hairs to regrow. There are no "treatments" that is guaranteed to hurry (or improve) this process. Only time will tell.
Its likely that without any intervention your hair will re-grow. But there is no way to know except with the test of time. You can try PRP treatments as they can't hurt and may help with the healing and re-growth process. If after 9 months the hair has not come back then at that point it will likely be permanent and you can look into surgical repair with a hair transplant or scalp micropigmentation.
There is some hair in that spot means damage is not serious.I think you will have your hair again a few couple of months without any permanent damage ..
Hair will regrow if there are follicles. I suggest seeing an expert to determine what treatments can be done to help. Best, Dr. Emer.
Many hair dressers that do not command the dying process and have a lot of experience, cause chemical burns that may not allow the hair to regrow. To make sure, wait 9 months and if the scar remains, the you may be stuck with it. If it is small, Scalp micropigmentation or hair transplants work well (see below)
if hair follicles are viable they should start regrowing by 4 months afer the injury. If there is no growth seek evaluation by a dermatologist ir a hair or burn specialist.
In general if you have a chemical burn to your scalp skin you will have symptoms of pain at the time of the burn. Alopecia areata is the most likely diagnosis for the description you give unless pain was associated at time of hair coloring. In any event you should see a dermatologist to take a more complete history and examine your scalp.
You require an up close exam by a dermatologist to figure out what's going on. This could be a burn but it could be several other things too.A dermatologist can tell you if the roots are still there - probably without needing to do a biopsy.