How to do multiple thumbnails, can also be magnified at the same time.

Hi. There is no such functionality built in K2. K2 items can have a gallery. This requires Simple Image Gallery Pro www.joomlaworks.net/extensions/commercial/simple-image-gallery-pro . However there is no zoom-in feature. You can see everything Simple Image Gallery Pro can do at the demo page at demo.joomlaworks.net/simple-image-gallery-pro . If it does not fit your needs you will have to search for a different plugin.