He acquired this wisdom only after much reading.

This wisdom was acquired by him only after much reading.

This wisdom will be acquired by him only after much reading.

This wisdom has been acquired by him only after much reading.

None of these

The sentence is in past tense ("acquired"), so the correct passive form uses "was acquired."

Past Indefinite Tense

Active voice: Subject + V2 + Object

Passive Voice: Object + was/were + V3 + by + Subject