I think 20 goals and 40-45 points are reasonable expectations for Patrik Laine to reach in his rookie season. He has an absolute cannon of a shot and will be centered by Mark Scheifele, Bryan Little or the vastly underrated Mathieu Perrault. The Jets have a very deep forward core - both down the middle and on the wing - so regardless of who he is with he should be able to produce.
It's possible he exceeds the totals I mentioned, obviously, but I'd be surprised if he does much more. Rookies don't come in and dominate the league like they used to and the Jets are in the NHL's hardest division so he'll get a steady dose of teams like Nashville, St. Louis, Chicago and Dallas. It's not going to be a cakewalk for Laine.
James Tanner
I find it hard to guess what a rookie's impact might be when I've never seen them play. So keeping in mind that this might not be the most informed guess I've ever made, I think Patrick Laine will score 30 goals and around 60 points as an NHL rookie.
The reasoning behind this is that everything I have read about him says that he is a pure sniper, and everything I know about the Jets makes me think they'll play him a lot as a rookie, shelter him when possible and put him on the PP a ton.