how do I know if bonjour has been installed on iMac

I am desperately trying to get my HP Photosmart C4780 to work again with iMac desktop running OS X Yosemite 10.10.4. It has worked on and off, never wirelessly, but with USB connection. The cable to the computer was annoyingly short, so we replaced it and now the computer doesn't seem to recognize the printer. Would Bonjour help me, and how do I install it if it is not already available on the computer? Thank You!!