As you say, the a9k is a router, so it kind of depends on your setup. If you have purely routed interfaces on the a9k towards DSLAMs, you can inspect the ARP table with 'show arp <interface>'.
If you are running a bridge domain/VPLS service on the a9k with mac-learning you can see this with 'show l2vpn forwarding bridge-domain XX:YY mac-address location X/Y/CPUZ'