Like SR, I can’t discern the red-&-black knot.
As for the other, it appears that a Slip-knot eye is indeed used
in some Trucker’s-Hitch tensioner, but the tie-off Half-hitches
are going the wrong way from the usual – back upwards vs.
downwards. This suggests that there is a 2nd rope-sheave
through which the rope runs additionally to this one, and
then it is tied off going upwards as shown (the 2nd sheave
being somewhere beneath what we see). !?
Or maybe not: I thought I saw 3 lines bending around the
white wood, but maybe there’s but 2. And the Half-hitching
could be directed upwards from the usual Trucker’s Hitch,
the end making a Half-hitch directly upon reeving through
the sheave around other line, rather than around itself.
Thanks for the observation.