what does "dick about squa"mean?
“So wondering why it takes a platoon of cops to arrest one man— one, since I happened to be with him, I know didn’t kill that poor man— is defensive because Eli and I are sleeping together?”
“I’m not criticizing you, honey.”
“Oh, bullshit!” Maureen exploded. “You’ve been standing around here pretending to feel sorry for Abra while gleefully questioning her judgment. And you’ve already arrested, tried and convicted Eli without knowing dick about squat.”
“I’m not the one suspected of murder—twice—or with police in my house. I don’t blame Abra, but—”

Question

what does "dick about squa"mean?
“So wondering why it takes a platoon of cops to arrest one man— one, since I happened to be with him, I know didn’t kill that poor man— is defensive because Eli and I are sleeping together?” 
“I’m not criticizing you, honey.” 
“Oh, bullshit!” Maureen exploded. “You’ve been standing around here pretending to feel sorry for Abra while gleefully questioning her judgment. And you’ve already arrested, tried and convicted Eli without knowing dick about squat.” 
“I’m not the one suspected of murder—twice—or with police in my house. I don’t blame Abra, but—”

Answer

"Dick" is a vulgar term referring to the male anatomy; however, here it is used to mean something along the lines of "nothing" or "anything".
"Squat" means nothing.
So, "without knowing dick about squat" is just emphasizing how little the person knows, in bit of an insulting manner. Yes, it is a bit weird if you look at each word individually, but overall this is its meaning.

Answer

"You don't know dick about squat" is an idiom.

It means "you don't know anything at all".