Sources will sometimes casually mention that this gun or that gun could penetrate the mantlet of a given tank at a given distance, or that a part on another tank was reinforced after the discovery of a flaw or weak spot in a portion of its armor.
Targeting weak points in opposing tanks is also an important part of gameplay in popular armor-themed video games such as War Thunder, Red Orchestra, Men of War, etc...
Of course, gamers today have access to far better information than ordinary soldiers seventy-plus years ago. At the same time, details like these do provide an edge in combat.
So how much of this kind of knowledge, if any, was used by tank crewmen during the conflict itself?
Were gunners simply taught to target center mass and hope for the best? Or were they well informed about the armor layout of enemy vehicles to the point that they would specifically, say, target an enemy Panther's mantlet or shot trap?
Or was the state of affairs somewhere in between, where a crewman might be educated about the proper engagement distance necessary to penetrate an enemy tank, but not know enough to deliberately target vulnerable locations?
As a general rule, it's 'position yourself to hit the side if you can, then aim center mass'. Hitting the target in the first place was hard enough.
However, it was certainly true that the tankers knew certain places to aim. I've seen in the archives the archetypal "Aim for the rounded underside of the Panther mantlet", for example, and a very curious document indicating it was standard practice for the 3" TDs in Italy to knock out Ferdinand/Elefants by ricocheting the round off the ground into their lower hull, so they really weren't all that scared of those supposed monsters.
More typically, though, the documentation put out would be simple enough estimates "At this range, you can punch through the turret at this distance, and the hull at that distance". Anything more finessed than that, such as the difference between the turret front and the mantlet, though certainly remarked upon in testing by the engineers, likely wasn't all that worried about by the crews as hitting the one vice the other would have been tricky. I have seen documentation which compares guns and ammunition on the basis that (Paraphrase) "dispersion was such as to make aiming at particular parts of the vehicle impractical", implying that aiming at particular parts was certainly a known technique.
On the Russian side, I recently ran across some articles discussing killing Ferdinands by aiming for the fuel tanks.
In the Red Army, there were propaganda pamphlets issued with instructions about where to aim specifically, either instructing gunners to hit for specific parts of the vehicle (fuel tanks, vision slits, etc) or just pointing out how far you can be to penetrate the side/front/turret/etc with a specific weapon: http://tankarchives.blogspot.ca/2013/06/weak-spots-and-hit-zones.html
For the Germans, I have not seen anything similar, but I'm sure it existed. For example this pre-war intelligence bulletin contains weak points of known Soviet tanks: http://tankarchives.blogspot.ca/2015/05/german-intel-red-army-tanks.html
Instructions regarding the T-34 and KV also made a difference between turret and hull armour: http://tankarchives.blogspot.ca/2014/01/german-analysis-of-t-34-and-kv.html
Of course, while these orders were issued and papers were printed, there is no way to tell if the crewmen actually read and remembered these figures. I recall a photo of a Tiger driver's plate with lots of dents and chips around the driver's visor and nowhere else, so presumably at least a few gunners retained this information.
It is the case that when a new system was fielded or modified, the US Army would put some subject matter experts into the field to provide actual hands on demonstrations or instruction. Case in point is when the 3" armed tank destroyers were fielded in Normandy, there were some accuracy "problems" whereupon the Aberdeen Proving Grounds sent over some civilian techs. One of whom consistently showed gunners how he could hit a German helmet at 1700 yards. Discussions about known vulnerabilities from field tests performed on site were also taught.