is it possible to use cnn models trained in cntk python in c#?
Yes, this is completely possible. The CNTK framework itself is written in C++ and the C# as well as the Python interface are only wrappers onto the C++ code. So, as long you use versions which are compatible to each other, you can do that. 
For instance, if you use CNTK 2.3.1 with python and also CNTK 2.3.1 with C# there is of course nothing which should get in your way. If the versions are different, it depends if there have been breaking changes.
Just for your information: There will be two formats in the near future: CNTK V2 model format and the new ONNX format.
I want to use CNTK python to train a CNN model and then use  the trained model when i am programming in c# or c++. Is it possible to use CNTK python 
trained model in C# or c++?