Can I use yogurt cheese in cheesecake by substituting the cream cheese?
I hope I am not making a wrong assumption here. But German quark is a soft cheese with somewhat creamy consistency which is made from a yogurt variety (or at least a cultured milk variety) . 

If "yoghurt cheese" is similar to quark in the way I think it is, you are probably better off not making a substitution, but use a recipe which was made for quark (or topfen, which is the Austrian word for the same cheese). They will probably give you a better result than a substitution. The search term to use would be Käsekuchen, this is the German version of cheesecake, and it is traditionally made with quark. If you cannot decipher a German recipe, I noticed that Google returns some results for "Käsekuchen recipe", you can specify results in English in the advanced search options if needed.