I'm counting the number of rows in a 1TB tplog using -11!(-2;`:tplog) internal function, which takes a long time as expected.
Is there a way to track progress (preferably as a percentage) of this operation?
No I don't believe this would be possible for the -2 option. It is possible with every other use of -11! by defining a custom .z.ps but it seems .z.ps isn't invoked when counting number of chunks.
Your best bet might be to check the raw file size on disk using a linux system command or using hcount and then based on some previous estimates tested on your machine you could create logic to come up with a ballpark estimate (maybe with a linear interpolation) of timing based only on the file size.
Of course - once you have the chunk count from the -2 option then you can easily create a progress estimate of an actual replay, just not for the chunk count part itself