"What is in the dolma?"
Translation:Dolmanın içinde ne var?
You could in theory say " içerisinde" with the possessive suffix, but it is much less common (I have never heard this myself). I added it.
Remember, the noun is "içeri" not "içer." You must add the possessive suffix to this :) If you use the possessive suffix and add a case marker, you need the buffer -n as well.