It should be on the ticket receipt emailed to you the day you booked the ticket on aa.com. U.S. law requires it.

With a U.S. destination you benefit from the Department of Transportation's single ticket/single allowance mandate even though you continue travel on Alaska Airlines. When you check in with Alaska for the return, they will honor AA's standard baggage allowance for your route (but are not required to give you AA's benefits to oneworld elites).