PHILADELPHIA — The Knicks and the 76ers have major health questions as the Eastern Conference semifinal series shifts to Xfinity Mobile Arena on Friday night.  The two centers, Joel Embiid and Mitchell Robinson, missed Game 2. Robinson (illness) is probable to return and Embiid (sprained right ankle, right hip soreness) is questionable. Knicks guard Josh Hart is also questionable due to a sprained left thumb.  Joel Embiid is pictured during the 76ers’ May 6 loss. Jason Szenes for the NY Post Hart suffered the injury late in the third quarter but was able to finish the game and play most of the final quarter.  Of the three, Embiid is likely the biggest question mark. On Tuesday, he woke up sore, 76ers coach Nick Nurse said, and the team determined after shootaround that day he wouldn’t be able to play. Andre Drummond started in Embiid’s place.  The oft-injured Embiid missed the first three games of the playoffs after undergoing an emergency appendectomy late in the regular season.…