If there are no train drivers trying to see this post it suggests a line not currently in use.
The other four possibilities still in use are roughly near Medlow Bath, Yerrinbool, between Mt Murray / Summit Tank, and Minnamurra.
The other lines which spring to mind near Sydney but abandoned are Camden and Kurrajong but neither was long enough to sport a 114 km post.
There is a possibility of a fifth but I do not know whether it ever boasted kilometer posts and that is the incomplete Maldon / Dombarton line. It seems unlikely that they ever erected kilometer posts on a line that never had track or even a complete roadbed given that a tunnel and two bridges were missing but stranger things have happened and the builders would have needed some means of establishing their position.
I will play your silly game and take a guess at "somewhere" on the Maldon Dombarton line. As to exactly where I do not know and even a guess would depend on which end they were planning to start the kilometerage from.
Edit: A review of the feasibility study for the line conducted in about 2009 indicates that the kilometer measurements would be from the Dombarton end and that 114 would be a couple of kilometers north of the Avon Passing Loop.
So my guess becomes a couple of kilometers north of the proposed Avon Passing Loop wherever the hell in the middle of nowhere to the east of Lake Avon that happens to be.