"What Features got Stored on it ?"

depends, on which of the 3 builtin recognizers you mean,

look at opencv\modules\contrib\src\facerec.cpp,

• eigenfaces
• fisherfaces
• LBPH

"how to read Stored Facial Features ?"

use a FileStorage object (again, look at the facerec src code)

also note, that some people might prefer to save as YML ( takes less space ) , so better not come up with your own xml parser.

"how to identify or know the extracted Facial features Using The Saved .xml model File ?"

don't you think, the FaceRecognizer class is the thing to use here ?

unless, ofc, you want to roll your own, and just grab the data