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- Avot keeping Mitzvot 9 answers
Rashi (to Bereishis 32:5) says that Yaakov kept the Torah in Lavan's house. Ramban (to 26:5) says that he only kept it inside Eretz Yisrael. Gur Aryeh (to 32:4 and 46:10) says he kept the Aseh's but not the Lo Sa'aseh's. The Ridvaz (Shu"t Ridvaz 696), Maharsha (Yoma 28b "mitzvosai"), Ohr HaChaim (to Bereishis 49:3), Da'as Zekeinim (to 37:35), and Nefesh HaChaim (1:21) all say that Yaakov kept all the Mitzvos.
Why do I give this lengthy background? Because of the fact that Yaakov mourned over Yosef's apparent demise. If Yaakov kept all of the mitzvos, then he would have had to write a Sefer Torah, as commanded in Devarim 31:19. In that Sefer Torah he would have written the fact that Yosef was alive. So how can you tell me that he didn't know that Yosef was alive?
I should clarify that many hold that Yaakov didn't keep the entire Torah. This question obviously wouldn't even start according to them.