QT and DQT are Kenwood's marketing terms for continuous tone-coded squelch and digital coded squelch. Motorola calls them "Private Line" and uses PL and DPL as the abbreviated monikers. GE called it "Channel Guard". It's all the same thing.
You'll need to find out what subaudible tone or digital code is being used on the repeaters you're wanting to access. Make sure you confirm whether a certain tone is used on transmit and receive. A few repeaters require a tone to access them but they don't transmit a tone. This is an issue because you won't be able to hear the repeater on your mobile radio unless you're monitoring in carrier squelch mode. The tone you programmed is blocking the carrier squelch repeater signal from your receiver. Other repeaters use a split tone, which means a different tone is used for transmit and receive.
You should be able to get ham frequencies and QT/DQT tones from fellow amateurs, radio clubs, or directories. If you're programming business or public safety frequencies (and you have the authority and permission to be on those frequencies) you can get the QT/DQT info from the agency's communications person or their radio vendor.
I'm honestly not sure on the OPT signal. Hopefully, another Kenwood user can fill us both in on that one.
Kenwood's TK-790 is a great radio. I own several in VHF and UHF and two of the high power remote models. You can't go wrong with the radio you chose. It's a real workhorse and they are available at very reasonable prices in the used market and online.
