“What was I looking for again?”
A coworker comes to your office to ask a question. You were supposed to search for some information for her on your computer, but you got sidetracked. You forgot what you were looking for. You say this to yourself.
What was I looking for again?
The phrase "look for" usually needs to have something after it:
I'm looking for a gift for my husband.
But in questions, that part comes earlier:
What are you looking for?
There's an old rule that some English teachers might try to enforce, which says that you shouldn't end a sentence with a preposition like "for". According to this rule, you're supposed to say or write:
For what are you looking?
But this is really strange and old-fashioned. You can use it in extremely formal writing, or maybe as a joke.
When you've forgotten what you were doing or saying, you use this phrase. It expresses to the listeners that you're trying to remember what to do. Some examples include:
Now, what was I searching for again? Oh yeah, last quarter's budget.
What were we talking about again?
You can also use the phrase "What was (something) again?" with a noun or a noun phrase to ask about things that you've forgotten and need to remember again:
What was his name again?
What was the address of the restaurant again?
When people use this phrase, the question is directed at themselves but of course they also want other people to hear it as well.