What is the meaning of "Lesor Sarav b'Nafsho""?
Rashi: This is an expression of endearment, like "v'Nefesh Yehonason Niksherah b'Nefesh David" (Shmuel I, 18:1). After he interpreted the dream, all endeared him.
Rashi (from Midrash Tehilim): The Kesiv is Saro 1 (singular); it refers to Potifar. Radak - Yosef commanded to incarcerate him.
Radak: He will have the power to restrict [Pharaoh's] officers and nobles, like Pharaoh did. "V'Al Picha Yishak Kol Ami Rak ha'Kisei Egdal Mimeka" - Yosef had full power, except for sitting on the throne.
Malbim: Pharaoh's final authorization of Yosef was "Ani Pharaoh u'Vil'adecha Lo Yarim Ish Es Yado v'Es Raglo b'Chol Eretz Mitzrayim" (Bereishis 41:44) - he elevated him [to run the country alone], above all his advisors and Chachamim - "u'Zkenav Yechakem." Malbim (Bereishis 41:44) - he could run the country alone, without asking Pharaoh or anyone else.
Minchas Shai: We do not find so in any Seforim. Also Mesores ha'Gedolah does not list this among words in which a Yud is omitted.
Why does it say "u'Zkenav Yechakem"?
Radak: Chachamim are called Zekenim, even if they are young, for normally Chachamim is found in elders - "bi'Yshishim Chachmah" (Iyov 12:12). Yosef was a Chacham, and he taught Pharaoh's Chachamim, for he was found to be wiser than them - "Ein Navon v'Chacham Kamocha" (Bereishis 41:39).
Malbim: Refer to 105:22:1:4.
