By “topics,” they mean forum threads. So you can get to 500 just by reading guild related threads, but it will be much faster if you click into other stuff too. You can also cheese the 20,000 read messages requirement by scrolling slowly through the megathreads. (High elf and vulpera threads are great for that.) I did it while watching YouTube videos.
To see where you are right now, click on your character portrait in the top right, and then on your name in the dropdown that comes up. You’ll be able to see your stats for most of these requirements.
To see your current trust level, use this URL.
Replace your name and realm in the URL, and then control+F trust. The realm is not capitalized. The highest trust number listed is your current level. (When you gain a new rank, it can take a few hours to update.)