Which sutta is it in which Sariputta asks his disciples .. friend if someone asks, is the world eternal
I found two that are similar, but not identical.

The Kalara Sutta is similar, in that it's Sariputta talking about Dependent Origination. However, in that sutta, it's the Buddha who is asking the questions; Sariputta has no disciples; and instead of asking whether the world is eternal, the question is whether birth is ended. This could perhaps be the one you're thinking of, because the Buddha asks questions like, "But, Sāriputta, if they were to ask you ..."

Or there's the The Greater Discourse on the
Elephant-Footprint Simile, which starts with Sariputta addressing the bhikkus as "Friends", and ends by repeating that "He who sees dependent origination sees the
Teaching; he who sees the Teaching sees dependent origination."