I just bought a old place with very poor upkeep.
The circuit breakers weren't labeled at all. I went
To label all of them and was able to determine all
Except for 2 that don't appear to go to anything.
Those 2 look different than the rest and I was
Wondering what they might be for.

They both take one slot and say 30A on the handle.
Next to the handle they say "10kA 120/240V~"
With a yellow D in a yellow box.
I haven't been able to figure out what that meant.

Thanks,
Adam

Sounds like a 2 pole 30 amp breaker, made by Square D. These are typically for water heater, dryer, cooktop, or a central air conditioner.

The "10kA 120/240V" means it is rated for 10,000 amps of short circuit interrupting capacity, too technical to explain for this forum, and of course, it is rated 120/240 volts.

The two breakers aren't connected.

There are dipole 240v breakers that take a single slot?

The only way for it to be 240v is if you have both legs. A single breaker will be 120v. Now that being said, I've seen people use two single pole breakers to get 240v if they didn't have a double pole. It's not right, but unfotunately lots of people do things that aren't right. They may even be spares, but unless you pull the panel face off you won't know. At this point you might want to find a professional to look at it. It's not as if simply removing the panel face will hurt you, BUT touching the wrong thing definitely could! Electricity is not something to take lightly.

There are double breakers that allow 2 single pole 120 circuits in one slot. Many single pole devices are rated for 240 volts perhaps including your breakers.

For now, perhaps leave them off and see if you find anything that is off.

A picture or a model number will help determine exactly what you have.

If you did remove panel cover, look where the unknown wires go out of the panel, then see if it goes in conduit with something else(washer?). Then maybe it was for dryer. Dryer was converted to Gas?
Just an example. Do wires exit the top or bottom of panel.
Leaving off not a bad idea. Hopefully in acouple of days you notice,
Looking in panel may help determine 120 or 240 volt circuit.
Verify it is #10 on the 30 amp breaker. If #12, it needs to be 20(or 15?)