Ohh that's a hard question. I think it would have to be what was his biggest regret? (After he had seen the reigns of his children). At the time of his reign he saw himself as God's chosen representative on Earth and of course many of his court would praise his desicions whether they agreed or not. Whilst there is evidence (as with much of history it's still up for debate) of him regretting Anne and Moors deaths for most of his reign he believed he was doing the right thing in God's eyes.

I think it would be interesting to see what he thought of his childrens reigns, for example would he regret how he treated Mary and thus her future devout Roman Catholism? Would he have arranged marriages as his children died heirless. Personally I think if he was going to regret anything it would be to do with his personal relationships with his wives and children rather than how he ran the country.

Ok I've just noticed my question unitentionally turned out quite similar to yours so maybe a slightly different question for variety's sake. If he could change one thing he did in his reign, what would it be and why? It could be anything from a decision, to changing advisors, (not)marrying different women etc.

I now appear to have rambled a bit, my apologies.