Hi

I have a little question. I must add id of the article / k2 item after title. It is that possibility?

Example: My first k2 item. 52 or 52 My first k2 item.

Anyone know how do this hack. Which file i must change, in which file i must seek?

Big thanks for help....

See here
getk2.org/documentation/tutorials/item/174-templating-with-k2-and-the-concepts-of-sub-templates
for a start.
Create an override, edit item and or category.php in the override files and add something like
this->item->id in the proper place (you might have to check for syntax