Savant

Savant is a formal word that refers to a learned person, especially someone with detailed knowledge about a particular subject. The word is also used to refer to a person affected with a developmental disorder who exhibits exceptional skill or brilliance in a particular subject or field.

His sister is a computer savant, so he knows he can call her whenever he has technical issues.

Sanskrit equivalent

विद्वान् / विशेषज्ञः