Risen

The number of chests opened are confirmed tracked between games. However, picking the same chest open a hundred times seems kinda counter-productive. I was able to get this during Chapter 1 and seldom reloaded a game too often where opening a locked chest would count twice. That means there is probably 100 or more chests available in the Chapter 1 game world alone, and you would be better off looting them all.

Opening chests with Lockpicks require the Open locks skill. Cid in Harbour Town will teach you this skill up to level 3 if you side with the Don. The combination is always the same, and always consist of an equal number of left or right picks. If you find yourself going through lockpicks too fast, save, get the combination, load and pick open the chest without expending lockpicks. Merchant selling lockpicks usually have a steady supply too, so don't be afraid to stock up.

 

A nice spot to boost this is in the Don's Treasury. There are three chests here (one next to the smoking girl, two on either side of his bed), and the combination will always be the same. Save just outside the first chest and then unlock them all (you'll be attacked), then simply load your save and repeat.