The question is not all that clear, and can and has been interpreted as:

-   How many Bitcointalk coders are there? (i.e. people that program Bitcointalk)
-   How many people, that are coders (wherever) are on bitcointalk?
-   How many Bitcoin Core coders are also on Bitcointalk?
-   How many Bitcoin Core coders are there?

Yesterday I went from interpreting the first option to the third, but now I believe you intended the second option. That is, to determine (a sample of) how many people that roam the forum, are actually coders, and probably more specifically, in an area related to bitcoin (and/or crypto in general).

Having a question so open to interpretation means that it should be readjusted for it to be of any use to you (otherwise it’s going to mix-up answers for all derivable interpretations).