This is a question, if ever you saw one.

I use this phrase. It’s to emphasize your point. Your example, “this is a question of you ever saw one,” is basically like saying the question is a doozy, or cannot be mistaken for something else.

I have heard it used to imply the item under discussion is a prime example of the type.

You might say to a friend in conversation, describing an attractive woman, “That woman was pretty.”

If the woman is the prettiest woman you have seen in a long time, you may say, “Now, that was a pretty girl, if ever you saw one.”

I more often hear it phrased using “I” rather than “you”. Perhaps it is local to my area: “Now that was a meal, if I ever had one.” would be a way to compliment a chef.

If I’ve told you once, I’ve told you a thousand times: it’s hyperbole.

It’s quite self-explanatory, nyet? If ever I saw one… ever being the key word. Makes it so special – ever, forever…

Roberta Flack sang The first time ever I saw your face.

And what TAFKAC said.