Which suffix (Pratyay) is used in the word 'Chhatri'?

The word 'Chhatri' is formed by adding the feminine/diminutive suffix 'ee' ($\text{ई}$) to the base noun 'Chhatra' ($\text{छत्र}$). Hence, the correct suffix is 'ee' ($\text{ई}$). Therefore, option B is correct.