can't make head nor tail of (someone or something)
Cannot understand someone or something at all; cannot make any sense of someone or something. I've been working with the new software for hours, but I still can't make head nor tail of it. I can't make head nor tail of that new guy in accounting. Sometimes, he's really friendly, and then other times he acts like he's never met me before.
can’t make head or/nor ˈtail of something
(informal) not be able to understand something at all: I can’t make head or tail of this picture — is it upside down?