My son is in the US as a student, when would he get his PR?

The timeline for your son's PR application depends on the chosen pathway and individual circumstances. He must maintain a valid non-immigrant visa, meet eligibility criteria, and adhere to specific application procedures. However, I recommend you consult with an immigration attorney

He may be eligible through self-petitioning as a person of extraordinary ability, employer sponsorship, adjusting status to a dual-intent visa, becoming an investor, or marrying a U.S. citizen or lawful permanent resident.

PR???

Oh you mean permanent residency. Well, that depends on the pathway and his personal circumstance.