Plugin "WP-PageNavi" doesnt works

what exactly is not working?
can you give a more accurate description?

how and where did you add the neccessary code?

assuming what still shows are the generic next_posts_link() and previous_posts_link() ?

There are no site numbers. Which code have I to add into the footer.php?

i am not sure that you would add the code into footer.php –

possibly into index.php where the existing page nav is;
at the bottom, a code section starting with
<nav id="nav-below">
or near the top, a section starting with:
<nav id="nav-above">

these might also be in a different template such as loop.php.

Which code have I to add

you should find this in the docu of the plugin, under ‘installation’.

Thanks. It works! There’s the line I needed:
<?php wp_pagenavi(); ?>

Greetings