How to know the boss??

If you see time running, click to see further details. Lots of time in my area it doesn't list the raid boss, but it will show the level at least! Happy hunting!

I think you have to position the cursor very close to the gym, and click the "scan" button (takes like 90 secs), so it will rescan the gym and update the gymhuntr data - then you should be able to see the Boss. That's what I remember, I've been in a FB messenger group the past 2 weeks and that's the best because I know if others will be there or not.

Or you could play the game how it's meant to be played and go there.

how are those scaners not violating niantic roules? After so much effort they got through to shut down the spwaning maps and all that players here screaming cheater whenever someone brought the map topic up. So this looks like tha same thing. Scaner accesing game data = violiation of code of conduct = cheating

Please stop using services like this. Niantic puts in a lot of effort to stop spoofers and cheaters, who contribute nothing to this game and only prevent niantic from developing the game.
You may not consider yourself a cheater but you are. Services like this are only possible because of spoofers constantly scanning the map and thus overloading niantic's servers.
You are supporting a system that is damaging the game, not to mention the unfair advantage you have over honest players.