"When will you see Raj?"
Translation:तू राज को कब देखेगा?
'को देखना' is grammatically similar to 'look at' with the postposition 'को' replacing the preposition 'at'.
Raj is in the oblique case. However, proper nouns don't change form. You can see it more clearly in the sentence 'तू राज के भाई को कब दिखेगा?' (When will you see Raj's brother) where 'राज का भाई' becomes 'राज के भाई' in the oblique case.