Need JQL for finding user in JIRA

I need the JQL to find the user in JIRA scope, apparently, once the user found, I need to assign the JIRA issue to that user.

Could anyone help me with this

Hi @Satya_Kishore,
The easiest way to train with JQL queries is to use the Jira itself. There is an option next to the search bar where you can switch to JQL search.

Using basic search you can define what you need and then switch to JQL where you will have part of query filled out already.