Printer not found

Mac OS X: About the Reset Printing System feature ...

http://support.apple.com/kb/HT1341?viewlocale=en_US

In System Preferences>Fax & Print, Right click or Control+click on the Printers list Sidebar, choose Reset Printing System.

if you hold option and click the "-" tab it resets the printing system.

http://www.macosxhints.com/article.php?story=20031215144430486

Safe Boot from the HD, (holding Shift key down at bootup).

Any devices that previously appeared in your Printer List and Fax List will need to be added again after resetting the printing system.

Resetting the printing system in Mac OS X

1. To use the Reset Printing System feature in Mac OS X, follow these steps:
2. Choose System Preferences from the Apple menu.
3. Choose Print & Fax from the View menu.
4. Control-click on list of printers on the left side of the window, then choose "Reset printing system" from the contextual menu. If you don't see a list of printers, Control-click on the text "Click + to add a printer or fax" and select "Reset printing system..."   
5. As an alternative, if you currently have one or more printers listed, you can Option-click the "-" (Remove printer) button.

http://support.apple.com/kb/ht1341

Reboot.

Is it connected by usb ethernet or wifi? You could try shutting down and restarting the printer or removing and re-adding it to the print queue. If it's through wifi you need to follow the instruction for the printer to reestablish the connection. The printer is not connected. It is thoug… - Apple Community

Hi,

Since this seems to be an AirPrint printer, I guess that the wired connection is via Ethernet to one of the LAN ports of a Wi-Fi router. Correct?

USB would require drivers, and Mac drivers do not appear to be available from Canon for this model.

https://www.usa.canon.com/internet/portal/us/home/support/details/printers/inkjet-multifunction/tr-series-inkjet/pixma-tr8620

With AirPrint, the following power-cycling sequence may be worth testing:

Power off the (Wi-Fi) router, the printer, the computer, and all other devices/computers. Wait two to three minutes. Power on the router. Wait two to three minutes. Power on the printer. Wait a minute or two. Power on the computer. Finally, power on all other devices/computers. Any change?

Addendum

According to the TR8600 series manual, this printer would also allow a USB connection to use the driverless AirPrint technology.

https://gdlp01.c-wss.com/gds/8/0300039988/02/TR8600ser_OnlineManual_Mac_EN_V02.pdf#mdg-c_pc_basic