Will rpr titer become negative after treatment? any lab test to proved that someone have fully treated and recovered from syphilis?

May not: The titer of the RPR will drop to very low levels if treated properly. There are other test that your doctor can order.

Usually becomes neg: The RPR usually returns to negative after successful treatment, but not always. But it always should become less strongly positive. If RPR starts with titer of, say, 1:64, within 6 months it should be 1:8 or lower. If not, the main lab test is a spinal tap to make sure no infection in spinal fluid. If RPR becomes negative, it is proof the treatment was effective; no other testing needed.