<p>I]The meeting shed light on the real personality of Jack who had asserted that…</p>
<p>this phrase is correct, the “who” refers to Jack (who was doing the asserting)</p>
<p>II]the meeting shed light on Jack’s real personality who had asserted that…</p>
<p>this phrase is incorrect because the “who” refers to “Jack’s real personality”, and it was Jack not his personality doing the asserting. Grammatically that is. His co-workers might have felt it was his personality :)</p>
<p>Anyway, I think that’s what you were asking…?</p>