However, depending on the context, it could be better translated as:
* "I don't know when you'd like to..." (if it's about a specific event or action)
* "I don't know when you want it." (if it's about a desired time for something)
* "I don't know when you're available." (if it's about a meeting or appointment)
To provide a more accurate translation, please provide me with the context of the phrase.