Obi-wan actually puts his hands on a lot of people's faces.
In Episode I, at the Invasion of Naboo, after Qui-Gon and Darth Maul's battle/death, Obi-wan is there for his master.
In Episode II, at the Battle of Geonosis, when the Jedi are surrounded by the droid army, he is seen with his hands on the face of a fallen Jedi.
In Episode III, on Mustafar, after Padme passes out from Anakin force choking her, Obi-wan puts his hand on her face.
I can only assume that he is checking on the person's condition by putting his hand on their face/forehead area. Possibly he is checking for a sign of life with this technique, similar to how we check for a pulse.