What is call back rate of RunUserNavAlgorithm() ?

The call back rate of RunUserNavAlgorithm() is defaulted to 200Hz.

The is controlled by the following line of code found in taskDataAcquisition.c

inertialAndPositionDataProcessing(dacRate)

dacRate is by default 200Hz

What is the max dacRate, where can I find a listing of possible dacRates?

I think users should not care about or change this.
This value should be the same as the calling rate of the task: TaskDataAcquisition.
If you want to change the algorithm calling rate, please refer to the implementation of
static void _Algorithm(uint16_t dacqRate, uint8_t algoType)
for details. You can see there how the EKF algorithm is called according to gAlgorithm.callingFreq.