There's 2 places you'll find the vulnerability information. First, on the main Websites screen to the right side, along with the other data points for things like Uptime, Backups etc.

The number of security vulnerabilities that need fixing is displayed next to a small padlock icon.

Second, if you click into a website and then go to WordPress > Vulnerabilities, you'll see the information here too.

It sure is! For a vulnerability that you no longer want to see, simply open the accordion and at the bottom, click the Permanently Ignore link.

You'll then be able to choose whether you want to ignore the vulnerability only for this website, or for all websites in your account.

Each vulnerability comes with a description on how to resolve it. So you simply need to follow the instructions on the screen (9 times out of 10, you just need to update the software to the latest version, eg. WordPress core, a plugin or a theme).

Yes, if you want them to be. Make sure you include the Security section when creating your client reports and any vulnerabilities you've resolved will be shown there.

Yep! Timeline (along with many other activities) will keep a record of every security vulnerability you resolve, on a website-by-website basis.