Confusing about the sentence structure

Gosh Pong, I'm no grammaticist (as you can plainly see) but I don't know of any such rule

what you were doing, and was in a sentence. it seems that does not make sense.

Sorry Pong, you'll have to reword that posting #….704

Your confusion comes from that silly notion that a sentence can only have one verb, Pongman. Where did you hear that?

That sentence, above, actually has four verbs [in bold] though two operate as one set.

Continuing the sentence, one can see that it's clearly a bogus rule.

You knew what you were doing was wrong when you came into the house carrying a bag that contained three donuts which had icing sugar sprinkled on them and candles stuck into them by that person who was living in the upstairs suite, the one who was married to Uncle Jim, the same person who ate the other three donuts before she got to the station that was now accepting full trains, ... .

pongman, There is no limit that I know of to the number of verbs that can be used in a sentence.

I sang and danced at the party while Mortimer ate everything in sight and drank too much.

Sorry, I am an ESL student. I am just confused of the sentence pattern of this sentence. "You knew what you were doing was wrong".

It's okay Pong. You can use as many verbs as you like

Let's try similar sentences.

"You knew that was wrong."
"You knew hitting your sister was wrong."
"You knew what you were doing was wrong."

"That", "hitting your sister" and "what you were doing" are all serving as the subject of the clause at the end. I'm sure I'm not explaining that the way an English teacher would but I hope you get the idea.

You / knew / what / was /wrong

You = subject
knew = main verb
what (you were doing) is the subject of the direct object clause
was = the verb of that clause
wrong = referral adjectve to what.

If you learn to diagram sentences, you will be able to understand English. But I have to tell you, your sentence is very complex.

Please explain what you find confusing about the sentence pattern, Pongman.

You could build it up:

I knew something.
I knew what I was doing
I knew something was wrong.
I knew what I was doing was wrong.

It's really not too puzzling when you look at the separate elements.