onomatopoeia for cluelessness

Question

Is there an オノマトペ for when you're absolutely clueless or expected to do something, but cannot?

Answer 1

ポカーン

seems like the closest to me. It is often associated with a blank stare.

jisho.org has vacantly; blankly; absentmindedly (​Onomatopoeic or mimetic word) as the definition of the root ぽかん.

Example images: ポカーン1 and ポカーン2

Answer 2

Two words popped up in my head as soon as I read the title.

1. 「さっぱり」

「さっぱりわからん。」 = "It's all Greek to me."

「何{なに}がなんだかさっぱり・・・」 = "No idea what the heck is going on here!"

2. 「チンプンカンプン」

This is a word many native speakers use actively, but I personally have never seen/heard a Japanese-learner use it.

It basically means "(Someone) has absolutely no idea.", "It's all Greek to (someone).", etc.

Some people might argue that 「チンプンカンプン」 is not an onomatopoeia as it seems to have Chinese roots.

For a layman like myself, however, I do feel that it is used like an onomatopoeia and it sounds like one as well.

Answer 3

If you have shocked feeling, something like trying to turn on the camera but no batteries in there. You can say "ガーン” or "ガビーン"

Σ(ﾟДﾟU)ガーン。で、電池が切れている。。。

In my opinion, オノマトペ is often accompanied with 顔文字{かおもじ}. The expression in the other answer also is expressed like

（´ρ｀）ぽか～ん

There might be some other suitable onomatopoeia for the future reference :【顔文字】　感情 / 表情　－　脱力 / 溜め息