Honestly, I can't really tell from that poor second render what poke through there is. But I am familiar with that Time for School outfit and there's a few things you can do to make it behave better.
Since the shirt, skirt, blazer and tie are all Dforce, you need to be constantly planning and thinking poses. I usually hide the tie and blazer and then simulate the shirt.... and adjust the skirt waist to fit it. Then I turn those objects into static objects and then simulate the blazer over top. If you leave everything as Dynamic, they tend to settle into each other. Instead, you need to turn off the Dforce on each layer after you finish it.
There's also an issue with the shirt sleeves that they poke through often. They even added a MAT option to hide the sleeves while leaving the cuffs visible to deal with this issue. I was just using Cutout Opacity to hide them before I saw the option in the menu, lol.
But basically those are the two main issues... turn on and off the Dforce settings as you simulate each layer and hide the sleeves when using the blazer. I also found the tie was pretty bad at Dforce, so I usually just manually moved it with Meshgrabber instead.
Finally, don't trust the Iray preview. It can show you a lot, but often misses some small things like poke-throughs and artifacts on the skin. Always best to run a quick 1 or 2 minute test render before committing your scene to a Queue.
