Breaking it down using using generalizations or to put it mildly, keep it simple stupid.
Clue -Watch your six: = look behind you, typically most of us will see the Milky Way when traveling to the Rift or while in the Rift depending on the angle. Is there something special we should see when looking back at the galaxy? A marker of some sorts?
Clue - The core of the problem: First we need to define the problem, which definition best meets this criteria?
1. Don't know exactly where to look.
2. Don't know exactly what were looking for?
1-a. Using the keyword "core" which is commonly known and referred to as the core of the galaxy this must be a play on words, therefore we can assume that core in this case means either, core of the rift, core of a sector, core of a system. Watching our six we can look behind us and see the core but this offers little help.
2-a. Thargoids or worse are most always referred to as coming from the rift or have been seen on the other side, therefore we can safely assume that we are looking for some kind of alien presence, ship wreckage, traces of their existence, or even them.
So the core problem can be narrowed down to 1-a where to look as 2.a provides enough information even though still vague.
Clue - The etymology of the name Kahina: Diviner or fortune teller, this clue is too ambiguous and is considered noise for now.
Clue - Formidine: Translated from Latin = Dread/Fear, no systems or areas equate into a similarity of the words dread/fear, there is a lot to be feared out in the rift, or the sense of dread when you hit a dead end but so far that's about it. This clue is noise for now.
Clue- Depends on who goes looking: This is just a reference on the nature of the individual who goes looking, do they have the patience, the willingness to search the enormous expanse, nothing special is required other than the ability to read between the lines of the clues given, and the sheer patience to keep at it.
Because of the sheer size of the area in question the Rift plus the outer arm, without any other substantial information this will take a very, very long time to find, it can't be the Bovomit sector as it is currently locked out, and I don't think the key to unlock has been in place since launch, or has it?
So to sum up all the madness, were looking for a system that has been accessible since launch that should in theory contain some sort of evidence of an alien presence.