I want to try generate DSM and DTM using Stereo Satellite Imagery (IKONOS, WorldView 4) and GCP file by Socet GXP.
You can get, provided you pay in most cases. I am not 100% certain but I think that IKONOS (or at the very least, one of the third party folks that rebundle the imagery) have stereo images available. A quick Google will provide a lot of sources and as far as I know certain older data is available for free.
Without proper ground control (as in post-processed GPS premarks) you are not going to get much in the way of accuracy, I'd reason anywhere between 30m on x and y and even more on z. The filtering of your point cloud will be a tough one too unless socketset has some handy texture based filters utilising multi-band to filter vegetation.
Is this purely an exercise you want to give a bash for educational purposes? If not, there are good sources of both free and paid elevation models out there.