Real neat creation with the "Forensics" use ! Very thoughtful addition !
That being said: My supposition would be that, if it is not otherwise indicated in a module/adventure, no training is required for that particular check; it can be attempted by anyone. What do others think ?
Also: As a larger point that is implied by this question --->
Page 144 in the Playtest rules, in the Skills section, says (in the fifth paragraph of the first column): "As the uses of a skill aren't comprehensive, there may be times when the GM asks you to attempt a skill check WITHOUT ANY OF THE LISTED ACTIONS, activities, free actions, or reactions ..." (My caps added for emphasis.)
This means that it's not always necessary in PF2 for there to be a specific "use" mentioned with a skill check. Skill checks can be made in a *general* way without a particular use. I think that is what is intended by Paizo for both this Medicine check (in area A4) and also the Thievery check in the pool room.
As another example: While there are lots of specific uses of the Athletics skill (shove, grapple, climb, etc.) described in the rules, there might certainly be a situation when someone is doing something Athletic that is not covered by the 10 uses outlined in the text. For example, suppose that an adventurer wanted to throw a bulky object over a wall. There isn't an Athletics use named Throw. In such a situation, I would think that you (at the behest of the GM) would make a general Athletics check, and the results of the check would be just: success = you accomplish the task, and failure = you don't, with no critical success or failure unless the adventure text (module creator) specifically mentions those.
Paizo moderators: Am I getting that right ?