expression
Used when the speaker is unsure or vague about what something is, often implying 'something or other' or 'some kind of thing'. Can appear in questions or statements expressing uncertainty.
彼は何事か言いたそうにしていた。
He seemed to want to say something or other.
何事かが起こったらしい。
It seems something (or other) happened.
何か is the common word for 'something', while 何事か adds a nuance of vagueness or uncertainty about the nature of the thing.
Compound of 何事 (nanigoto, 'what thing') + か (ka, question particle). The combination yields a meaning of 'something or other'.