You have to use USQL:
Using such query you can find all sessions that contains particular action according to your needs.
Sebastian is correct, you can do this using USQL. Specifically if you pull data from the usersession table, and check that there is a useraction.name matching the action you are interested in, it will return all user sessions that include that particular action. Here is an example:
SELECT COUNT(*), browserFamily
WHERE useraction.name = "/easytravel/rest/journeys/"
GROUP BY browserFamily
This will return the count of user sessions, split by browser, that contain the user action "/easytravel/rest/journeys/". Once you get this down you can play around with the metrics you are bringing in to chart exactly what you would like.