Ansys Employee
The documentation goes in some aspects into what you are asking.

1/Getting TKE using some sanity checks. C programming + some Fluent Predefined variables.
2/The two others terms are not documented but what I can understand is that the second one requires your return value for the drift coefficient and the other ones is not required as you are not adding term into the continuity equation.

I can double check the meaning of those terms. I will write back if I have something different to share but I am confident what I wrote is correct.