What makes you think that Trump really didn’t know about Sessions’ recusal beforehand?
Trump said he was not apprised of Sessions recusal at any point. Even the time when Sessions announced it. It was made public and POTUS had to react. Trump was so mad that it eventually brought Sessions offer to resign, is the way I remember it.
That was when Trump started complaining about the lost opportunity to nominate someone else, “if Sessions knew he was going to recuse”. I took that to mean POTUS thought Sessions must have weighed the possibility of recusing before he ever took his seat. I believe he recused two days later from all things Russia. Or, very soon after seated at JD. No?