Where can user see all questions they are following?

Since 2.4, it can be viewed in Activity feed. Also all other subscription like category, user can be seen in activity feed.

How do I add a sub-page to the [anspress] shortcode?

Check here: https://github.com/anspress/anspress/blob/master/includes/common-pages.php#L41

Avatar is not showing

i had the same issue. buddypress avatar overwrite anspress avatar functionality. so if you upload avatar from buddypress profile, then your avatar would display in anspress.

Counting char in Turkish language is not working

Try our recent commit, https://github.com/anspress/anspress/archive/master.zip along with recent tags extension: https://github.com/anspress/tags-for-anspress/archive/master.zip

New @ Mention feature has some bugs I think

Try the latest commit https://github.com/anspress/anspress/archive/master.zip, its almost stable .

HELP! I need hide the username of the user! Please check the image attached.

There is an option in AnsPress option to hide hover card.