I don't have the keyboard to show it, but the nasal n, as in here, there, where, and yes, NEVER has audio on the app in these particular types exercises. This is a big problem in the app that needs to be fixed!! Please don't let Hindi be the ugly stepchild language on the app.
The audio seems correct.
Note that the nasal that is denoted by ँ is not really the nasal consonant 'n' (though it's sometimes transliterated that way in English). It is telling you that the vowel it is placed over must be nasalised (think French).
In कहाँ, this means you pronounce it as kahā but the last 'ā' sound must come from your nose as well as your mouth.