Is it possible to get stevens johnson syndrome twice?

Yes, unfortunately: Patients with stevens johnson syndrome can recover and later, even years later, get it again. If the first sjs episode was caused by a known medication, the patient must avoid that medication and similar, related drugs. Some patients may have a genetic pre-disposition (inborn likelihood) to get sjs, which increases their chances of getting it a second time.

Yes: Unfortunately, yes, it is possible.