From where i can set the title of the attachment page?

It’s the title of the image in your Media Library.

yes, but with the blog name before and after the image name
it looks kinda spammy

hm infact its showing the post/page name, then the image name, then the blog name
and if you are targeting one keyword, it does look spammy
removing the blog name at the end would help a lot
while the seo plugin can be used to set those for msot other pages, it doesnt work for the attachament page

so do we have a way to modify just the attachment page title creation?

You could edit the attachment.php or image.php (depening on your theme.

hm i’ve got a template without both, i guess they are using the post page template?

from the Template Hierachy:

Attachment Templates:

• 1. MIME_type.php – it can be any MIME type (image.php, video.php, audio.php, application.php or any other).
• 2. attachment.php
• 3. single.php
• 4. index.php

If you don’t have an attachment.php or image.php in your theme it uses single.php or index.php.
You can always duplicate single.php and rename it to attachement.php and edit according to your needs