know the parameter of common mode choke for power adapter
You should first measure the conducted emissions of your device to the mains. Based on those readings you can identify which frequency components you wish to attenuate (referr to one of these limits to check what are the maximum emission levels).

Once you've identified what do you wish to attenuate I suggest you take a look at this:



Common Mode Chokes usually have this graph in the datasheet:



In its common configuration (black line in this case) you'll see if it will propperly attenuate your target frequencies. If you want to attenuate outside of the reach of the CM Choke, take a look at the filter structure picture before, you'll identify which elements tend to affect which frequencies.