If you wish to auto-discover printers on mobile devices you will need to activate Bonjour forwarding on your SSID's.
Step 1: Make sure the VLAN where the printers are residing are also allowed on the switchports leading to your AP's.
Step 2: Go to the page Wireless -> Access Control and make sure the correct SSID is selected.
Step 3: Near the bottom of that page you will see the option to enable Bonjour Gateway, enable it and then you will have the option to add a service. So add description printers, add the service VLAN (which is the VLAN where the printers are in and then don't forget to enable at least the printers service.