How can Quora authors see their Quora PeopleRank change over time on a graph?

You can’t. Refer How can I see my Quora PeopleRank? PeopleRank values and the PeopleRank algorithm is not divulged, although there are good guesses about what it involves.

And given that Quora Stats has been broken for years, even if Quora did release people’s PeopleRank, you likely still wouldn’t be able to see it.