In the case of Adam and Kayin, G-d asks both of them questions of which He is already aware of the answers, in order not to overwhelm them with what He was going to say.
It is therefore possible, that since here in Parshas Vayigash, in the instance of Yosef having just made a shocking revelation to his brothers, one can understand that the reason he asked, “Is my father still alive?” was not because he needed to know, but because he wanted to enter the conversation with them in a mild manner.
Consequently, it can be assumed that the reason Rashi was not bothered by this question was because he relied on his previous explanations about Adam and Kayin, and presumed that anyone who was learning the Torah would draw the same conclusion as found in those instances.
The difficulty
In our case, however, this does not seem to be an adequate explanation.
Yosef and his brothers had already been speaking at length about his father during the detailed conversation regarding Yaakov’s hesitation to send Binyamin, and it was already quite clear that his father was alive. It is therefore difficult to explain that this subject would serve as a conversation starter.
If he was merely looking for an ice-breaker, why use a question that his brothers had already answered? If indeed he was looking for a mild way to begin the conversation, he should have done so with another topic, rather than a subject which they had already been discussing at length.
It is therefore safe to assume that the meaning of his question, “Is my father still alive?” had some other intent, which too, was already clear from an earlier place in the Torah, and therefore Rashi saw no need to mention the question.
