Here you can find some most popular search examples. Just copy and paste with some modifications into the textarea: 

Image Modified

Find by Comment Author

...

{
  "issue.fields.issuelinks": {
    "$elemMatch": {
      "type.name": "Blocks",
      "inwardIssue.key": {"$regex": "MORPH-"},
      "inwardIssue.fields.status.name": {
        "$nin": [
          "Closed",
          "Resolved"
        ]
      }
    }
  }
}

Reusing Results from Previous Search Query

It is also possible to use array of search queries, passing the "__RESULT__" keyword (which contains issues keys from the previous query) into the second query.

[{...}, {...}]

For example, the query below would read like this (from second to first):

Find Tasks with link type "Blocks" and which are not blocking Stories where some@gmail.com has left a comment

[{
  "fields.issuetype.name": "Story",
  "fields.comment.comments.author.emailAddress": "some@gmail.com"
},
{
  "fields.issuelinks.outwardIssue.fields.issuetype.name": "Task",
  "fields.issuelinks.type.name": "Blocks",
  "fields.issuelinks.outwardIssue.key": {"$nin": "__RESULT__"}
}]

All keys from the first query will be passed instead of the __RESULT__ into the second query.