Phrasing a sentence "Do you know any people whom I could combine my efforts with?"

Question

I'm composing a sentence and I have doubts on whether it's correctly formed. First I wrote

1. "Do you know any people whom I could combine my efforts with?"

than I thought nah, that's not right, and wrote

2. "Do you know any people that I could combine my efforts with?"

but that "that" also didn't feel right so I went with

3. "Do you know any people I could combine my efforts with?"

What would be the proper way to phrase it? Thank you.

Answer 1

The first is nearly correct, but it is conventional to put the preposition with before whom:

Do you know any people with whom I could combine my efforts?

Here is a question from EL&U that justifies the use of whom, and incidentally shows where to put the preposition.

Your second option is correct but somewhat unsatisfactory: it is just a way of avoiding the issue of whom.

The third is also correct and equally unsatisfactory: it is the same as the second apart from exercising the option to drop the relative pronoun that. This is just a personal opinion, but I think that it's OK to exercise this option in spoken English but it's a bit slack for formal, written English.

Note that there is no option to drop the reltive pronoun who or whom.

Answer 2

Your third sentence

Do you know any people I could combine my efforts with?

is correct. Your first sentence is not far off, but could be

Do you know any people with whom I could combine my efforts?

Your sens is correct about the second sentence, since you are asking about a person, "that" is awkward to use.