How to get the date when issue was Assigned to a person through JQL

[shruti]

By JQL I want to know the date when the issue was assigned to a particular person

[Jobin Kuruvilla [Adaptavist]]

You need to capture that date in a custom field if you want to pull it into the search results. Since you are looking at the date when the issue is assigned, you will have to listen on the "Issue Assigned" event in a plugin. 

Date of workflow transitions would have been easier since there are plugins that can set the current date on a custom field during workflow transitions.

[Thomas Schlegel]

JQL is no SQL, you can't query a date, just a list of issues.