na-adjective
puzzled; perplexed; suspicious
Describes a feeling of doubt or suspicion when something seems off or hard to understand. Often used with ～な顔, ～そうに, or ～に思う.
彼は怪訝な顔で私を見た。
He looked at me with a puzzled expression.
その説明を聞いて、私は怪訝に思った。
Hearing that explanation, I felt suspicious.
Compound of 怪 (kai, 'suspicious') and 訝 (ge, 'doubtful'). The reading けげん is the kan'on reading of both characters.