PokerTracker

Where can I find a detailed description of how each HUD stat is calculated?
For example, I want to know how the "positional awareness" stat is calculated

Go to Configure > Statistics. Here you can see detailed descriptions of all built-in stats.

Custom Statistics Guide

Not available for trial version...
Is there an online version or some other way?

Not yet. Positional awareness is defined as follows:

Ratio of the times a player opened the pot with a raise on the button to the times they opened the pot with a raise in early position.

Formula: (Number of Times Player Raised First in on the Button / Number of Times Player Could Raise First in on the Button) / (Number of Times Player Raised First in in Early Position / Number of Times Player Could Raise First in in Early Position)