Even if the discussions are locked, it doesn't mean that you can't read what's already there. It only means that you can't post questions of your own.

I've found that, even if I can no longer contribute to sentence discussions, the questions that I've wanted to ask have already been asked.

Since you didn't mention any one sentence with "rien du tout" as one you're struggling with, I've found one from Duolingo online:

"I don't understand anything at all."

Correct answer: Je ne comprends rien du tout.

The locked sentence discussion: https://forum.duolingo.com/comment/32728547/I-don-t-understand-anything-at-all

The first comment on it:

"Why is it "du tout" not "de tout"?"

The reply to that person's question:

"French nouns are used with their articles in most situations, like 'I hate French grammar' is 'je déteste la grammaire française'.

The French way of saying 'anything at all' is 'anything of the everything', 'le tout' being the noun for everything or 'all of it' - so we have 'rien du tout'.

You can have 'de tout' in other usages where tout is not a noun, eg 'Je ne comprends rien de tout cela' - 'I don't understand any of that' ('I don't understand anything of all that')."

And, I mean, failing that, have you ever considered just trying to google your question? Here's something I got from looking up "du tout or de tout":

https://french.stackexchange.com/questions/9499/lutilisation-de-du-dans-pas-du-tout