You can either retrieve all extra fields at the same time (in a foreach loop) or separately. You can't have more than 1 set of extra fields displayed directly in a K2 item by default. My guess is that you want to split them in small batches, so just retrieve each extra field by its alias value. How? Read below:

=== Call specific extra fields in K2 templates ===
So how would you directly output individual extra fields in your K2 overrides? Simple. Just do something like this (e.g. in item.php) to get the extra field name:

$this->item->extraFields->EXTRAFIELD_ALIAS_HERE->name

To get the extra field value you would simply do this:

$this->item->extraFields->EXTRAFIELD_ALIAS_HERE->value
$this->item->extraFields->EXTRAFIELD_ALIAS_HERE->rawValue (for date type only)

Simply replace EXTRAFIELD_ALIAS_HERE with the actual alias of the extra field you wish to output.

In modules, use:

$item->extraFields->EXTRAFIELD_ALIAS_HERE->value
$item->extraFields->EXTRAFIELD_ALIAS_HERE->rawValue (for date type only)