וַיִּקַּ֣ח יוֹסֵף֮ אֶת־שְׁנֵיהֶם֒ אֶת־אֶפְרַ֤יִם בִּֽימִינוֹ֙ מִשְּׂמֹ֣אל יִשְׂרָאֵ֔ל וְאֶת־מְנַשֶּׁ֥ה בִשְׂמֹאל֖וֹ מִימִ֣ין יִשְׂרָאֵ֑ל וַיַּגֵּ֖שׁ אֵלָֽיו׃
And Joseph took them both, Ephraim in his right hand toward Israel’s left hand, and Manasseh in his left hand toward Israel’s right hand, and brought them near unto him.
Rashi on Genesis
את אפרים בימינו משמאל ישראל EPHRAIM ON HIS RIGHT HAND TOWARDS ISRAEL’S LEFT — If one is moving towards another person his right hand is opposite the other’s left. Now since he (Manasseh) was the first-born he was marked out for the blessing and should have been placed at Jacob’s right hand.
Rashbam on Genesis
את אפרים בימינו, in order to place him on Israel’s left side, (seeing he was the younger).
Radak on Genesis
בימינו, on Joseph’s right, which was the left side of Yaakov (Yisrael)