First place a Repeating Command Block (*always active, no matter where the arrow points)
Then type (copy and paste) this command:
execute @a[​tag=gamemodeView] ~~~ titleraw @s actionbar {"rawtext":[{"text":"§6A§2d§3r§4ian's §r§oADMIN-View"},{"text":"\n§rSurvival: "},{"selector":"@a[​m=s]"},{"text":"\n§l§3Creative: "},{"selector":"@a[​m=c]"},{"text":"\n§o§4Adventure: "},{"selector":"@a[​m=a]"}]}

At last you enter (copy and paste) this Command in the chat:
/tag @s add gamemodeView
Done, now you have a (Admin) Gamemode View!
Sorry, but I have to learn to display the number of players instead of their names!