What are the connotations of "Vayar Adonav... Ki Hashem Imo"?
Rashi: His master saw that Hashem's Name was constantly 'on his tongue' 1 - a clear indication that all his successes were Divinely inspired.
Ramban #1: He saw that he succeeded in everything that he undertook over and above the normal success-rate, and he attributed it to Divine assistance.
Ramban #2 (from Bereishis Rabah 86:5): He actually saw that the Shechinah was with him. 2
Targum Onkelos and Targum Yonasan: Refer to 39:2:1:1
Seforno: Refer to 39:2:1:2.
Malbim: Even though Yosef was also Ish Matzli'ach (had natural success), Potifar noted only Ki Hashem Imo (his supernatural success). I.e. Yosef succeeded in 'Kol Asher Hu Oseh' - even things that by nature should not succeed.
Ha'Emek Davar: He realized that the success is because Hashem was with him, for only what was b'Yado (under Yosef's jurisdiction) succeeded.