In the last question I said that I do not believe he should discontinue his University, but at the same time I do think it will be a weakness his opponents can exploit. Not only can they, but they will exploit him on this as a weakness. Though I do not think he should be forced to discontinue it, I do think that it is something his opponents can skew to say he does not have time for his university and his campaign let alone a presidential position.
In light of the issues surrounding Trump University, it is one of several issues that opponents can exploit. Trump has no political experience, but is experienced in political dealing. His stances on issues have changed over the years, meaning he has no political core, but approaches things mroe for political expedience. All that combined can be exploited.
Yes, Trump University will definitely be one weakness Trump's opponents can and likely will exploit. It is one example of dishonest and possibly criminal actions on his part. However, it may not make a huge difference. For whatever reason, Trump's dishonesty, vulgarity and general missteps don't seem to deter his supporters.
If Trump University were a weakness his opponents would have exploited it already and Trump would not be in the lead. His university clearly isn't an issue for his supporters and he has too big of a lead for this non-issue to matter now. His opponents are clutching at straws since they are losing.