A colloquial expression meaning that things are so confused you can't tell what's going on or make sense of the situation.
会議の説明が早すぎて、何が何だかわからない。
The explanation at the meeting was too fast, and I couldn't make heads or tails of it.
急な変更で、みんな何が何だかわからない様子だった。
With the sudden change, everyone seemed completely unsure of what was going on.
説明書が不十分で組み立て方が何が何だかわからない。
The instructions were insufficient, so I couldn't figure out how to assemble it.