In this example we want to count all Bugs linked to the issue and when clicking on the number we want to get to see all these issues in the issue navigator.
For this a Calculated Text Field is needed. The configuration will look like this:
Text to be parsed is: "<a href='"+%{00169}+"/issues/?jql=issue%20in%20linkedIssues(\""+%{00015}+"\")%20and%20type%3DBug'>" + count(filterByIssueType(linkedIssues(),"Bug")) + "</a>"
Note that:
Once configured and added to the issue, the issue screen will look like this:
Clicking on the number resulting from the custom field (in this case "2"), will link to the issue navigator: