1. I'll probably go and check out that apple, actually.

2. I'll probably go and check that apple, actually.

3. I'll probably go and check on that apple, actually.
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Which one is correct? Do we have to use 'out' after 'check' here?

4. The waitress who served in/at the restaurant was very unkind.
(Do we have to use 'in' or 'at'? Are both OK? Then, which one is commonly used?)

1 answer

1, 2, and 3 -- I'd omit "and" and "actually."
Otherwise, all are fine.

4 -- I'd omit "who served in/at" because the clause is redundant -- if she a waitress in that restaurant, then serving is what she does. You might want to write, "The tall waitress in [or "at"] Mario's was very unkind." The preposition used could be either one.