* कब (kab) - This is the most common word for "when" and is used for asking about a time or point in time. Example: "कब आएंगे?" (kab aayenge?) - When will you come?
* जब (jab) - This is used for "when" as a conjunction, indicating a time or condition. Example: "जब मैं आया, तो वह सो रहा था." (jab main aaya, to vah so raha tha.) - When I arrived, he was sleeping.
* किस समय (kis samay) - This translates to "at what time" and is used for asking about a specific time. Example: "किस समय बस आएगी?" (kis samay bus aayegi?) - At what time will the bus come?
The best translation depends on the sentence you want to construct.