(I was sure I asked the question quite some time ago, but unless i used a different account its not in my previous topics ...)

Looking at SEO using Joomla! 3.4.8 and K2 (v2.6.9), i`d like to have more control over the page title, at the moment the construct seems to be

URL : domain.com/{k2-menu-item-alias)/item/{k2itemid}-{k2-item-alias}
Title : Site Name - {k2-item-title} (site name placement from Joomla! Global Config.)

I`d like to get the k2-menu-item-title into the page Title, eg :

Title : Site Name - {k2-menu-item-title} - {k2-item-title}

Where to achieve it through editing K2 core files ? K2 settings ?

You can do this from a plugin or the simplest way would be through your template's overrides.

docs.joomla.org/Customising_the_dynamic_page_title