1. identify or remember the details of something
I just can't put my finger on it
If you 'can't put your finger on' something it means not to know, be able to identify what is wrong, or what is different or unusual about a situation or matter. "I couldn't quite put my finger on what age he was." "Something seems strange about the room, but I couldn't put my finger on it." You can use this expression in social and professional situations.