I want to use isset() in if() to display something if a zenpage is displayed. Is there a variable, such as $_zp_current_album for a currently displayed ZenPage?

Or should I use another way?

here is $_zp_gallery_page which is set to the script that is being run, e.g. album.php, pages.php, etc.

But if I need to display smthng on pages but not on albums?

Sorry, what is your question. I did answer how you know what script is running. That should be enough for you to make your if test.

You can find all Zenpage related functions here:
zp-core -> extensions -> zenpage -> zenpage-template-functions.php.

I guess you're looking for the function is_Pages() which checks if the current page is a zenpage page.

Also Zenpage pages have their own theme file pages.php where you would have to place the checks you need. There is of course also a equivalent to $_zp_current_album which is $_zp_current_zenpage_page. (all listed on the user guide global variable article).