Yes and no. Forget about "either" for a moment, that's not the bigger issue. In general, you would not use "the car" and "cat" together like that ("the car, cat" <-- notice a space after a comma). I don't know much about the car or the cat = correct I don't know much about the car or cat = correct ^^^^^^^.... the car or cat = the (car or cat) Examples with "either": 1. You and I are talking about horses. I tell you I don't know anything about horses. And you say, what about cars and cats? And I say, "I don't know much about cars or cats either". = I don't know anything about cars, and I don't know anything about cats and in addition to not knowing anything about cars and cats, I also don't know anything about horses. 2a. I don't know anything about cars. Cats either. 2b. I don't know anything about cars, cats either. 2c. I don't know anything about cars -- cats either. ^^^^ all the above = I don't know anything about cars and I don't know anything about cats. 3a. I don't know anything about the car or the cat. 3b. I don't know anything about the car or cat. ^^^^^^^ both mean the *specific* car and the *specific* cat that we were talking about. 4a. I don't know anything about the car or the cat either. = I don't know anything about the car and I don't know anything about the cat. 4b. I don't know anything about the car or cat either. = I don't know anything about (the car and the cat) in addition to something else (x), horses maybe. Basically, the problem isn't "either", it's ("the car, cat")

The correct sentence is either "I don't know much about cars. Cats neither." or "I don't know much about cars. Not cats either." "Either" is used to indicate a choice between two options. English "or" generally doesn't distinguish inclusive or exclusive "or" e.g. "A or B" could mean "A, B, or both", or "A or B, but not both". This means that a lot of the time both "还是" and "或者" can be translated as "or" ("还是" also makes a sentence a question, which is a property not shared with "either"). E.g. A: Do you like cats or dogs? B: I like dogs. A: Do you like cats or dogs? B: Yes. Both answers are possible because "Do you like cats or dogs?" can mean both "你喜欢狗还是猫?" or "你喜欢狗或者猫吗?". Most of the time what exactly the question means can be inferred from the context. "Either" can be used to clarify that the person asking it wants "yes" or "no" as an answer i.e. you could only answer "Do you like either cats or dogs?" with "yes" or "no". In a positive sentence, the structure "either A or B" is used to indicate that you mean exclusive "or". I reckon "or" is exclusive most of the time without "either" anyway, outside of programming at least. Adding "either" does however reduce any ambiguity. If you said something like "I think he likes tea or coffee", there's a possibility that he likes both tea and coffee. Saying "I think he likes either tea or coffee" means that I think he likes one of tea or coffee, but not both.

You're using "either" perfectly. It's the definite article that has to go. "I don't know much about [ ] cars or cats either."

Thank you! @Omar @Ruslan

I don't want either of them