The only 2 ways I know of finding out are to use TubeBuddy or to right click on the page when their video is up and click 'View Page Source' then you ctrl + F to find the tags, but I don't think you can do either of those things on Android
It's an extension you can use to help you with YouTube, there is a free service, paid, then last option is boosted which costs money, the prices can be viewed here: https://vidiq.com/plans/
If you guys want a PC one, I heard you can press F12 on the video page and search the coding until you find the tags. It's the most ineffective way but if you are uncomfortable with downloading stuff to your pc and such this is a crappy alternative that might yield results. VidIQ is actually the best. I have it now and wish I had it earlier on.
As most of our freedom family friends said, vidIQ and TubeBuddy are the well known extensions for getting tags used in a video and suggestions for new tags for your video during upload.