So you're looking for precise sectors or something?
Unfortunately, it'll most likely be different for every HDD/OS...
It all depends on partition structure and where the OS has decided to store the data within the partition/file system when it was being persisted to the disk... If you can't recover the file system because the HDD failed and it was all corrupted, you're going to struggle to be able to find a "wallet.dat" as such. Without the file system (which is essentially a map of where everything is stored on the disk), it's all just a collection of 1s and 0s
Even doing a sector by sector scan looking for certain byte sequences is not 100% accurate as their is no guarantee that the data was actually stored on the disk in a contiguous manner.