Tom menunjuk kursi disebelahnya.

English Translation

Tom pointed to the chair next to his.

The Indonesian sentence has two problems.

  1. “Disebelah” should be “di sebelah” in two words.
  2. “Di sebelahNYA” means “next to HIM”, not “next to HIS”.

I think

Tom menunjuk kursi di sebelah kursinya.
Tom menunjuk kursi di sebelah miliknya.
would be much better.