"He found sand in the shoe."
Translation:O, ayakkabının içinde kum buldu.
yes but that could also be on the shoe, it doesn't necessarily mean that it was inside
It is ayakkabıda. You're right that it should have an "n", but it doesn't. Some words are merged to such an extent that they're not perceived as compound nouns anymore, in standard Turkish.
In my dialect, we say "pazartesine kadar" for example, but the correct form nowadays is "pazartesiYe kadar". My grandma could say "kahvaltıNdan sonra dışarı çıktım" with an N, which is also not done in today's Turkish.
So, how do you say "he found sand in YOUR shoe/shoes"? Just the same as this?
"Senin ayakkabının içinde ❤❤❤ buldu." We use the necessary possesive pronoun(senin) to prevent confusion between the second and the third singular person.