If you want to hear the word “Mekaddishkem” pronounced correctly, you need to listen to someone who speaks Hebrew. Here is a female from Israel pronouncing the word Mekaddishkem.
As you will probably be able to hear, it is not the first section of the word that is difficult to pronounce, but the ending, which contains the “-kem”. In English, this would be pronounced with a hard K sound, but in Hebrew, there is a more guttural sound to it.
It can take a few tries before you get it right, so do not give up just yet. It helps to listen to the sound a few times before you attempt to pronounce it on your own.
If you are having any difficulties, simply visit a temple in your area and ask the Rabbi for some assistance.