Given the number of athletes all time, having this magical wish for just one athlete won't really bring much extra knowledge about the broader topic of doping in T&F. The important questions are prevalence, and performance benefit.
On a side note, framing the wish in terms of PEDs is ambiguous, given that some known or suspected PEDs have always been WADA legal, and some WADA banned drugs aren't known to be performance enhancing.
The more interesting question for me though is not any rule violation itself, but the performance aspect of having taken a PED. Do we also get to find out if the PED worked, for each and every event of interest, and how much the PED helped compared to a scenario without the PED? What about multiple PEDs? Will we also know the individual contribution of each, and any synergistic bonus of combining multiple PEDs?
Do we find out the mechanism of performance benefit? Is there really a physical enhancement directly attributlable to the PED, or is it indirect, due to psychological changes and placebo effect, or both? Expanding on that idea, can we also find out the compartive benefit of other mechanisms, such as growing up, living, and/or training at altitude, or changes in coaching and training and diet, or simply the cumulative effect of many years of training, and external changes such as running surface, shoes, strategies of hydration and energy replenishment?
Just knowing if they "used", and how many times, doesn't seem all that interesting on its own.