Siebe’s questions:
” i am curious how one can experience infiniteness?”
If and when I experience it, I will try to explain it.
“Is there a difference between a certain vinnana (for example sota-vinnana) and vinnana-dhatu? Is there a relationship?
Of course there is. It is like asking whether there is a relationship between patavi dhatu and a tree or house.
“I understood vinnana is something that conditionally arises and ceases, dependend for example on sense-contact. Is vinnana-dhatu not something that arises and ceases?”
The problem here is that you (and many others I have seen at the Dhamma Wheel forum), just use terms without trying to understand the real meaning.
For example, when you say, “vinnana is something that conditionally arises and ceases, dependend for example on sense-contact.”, that is a lot of words without much essence.
Try to understand (and express in your own terms) what happens in the case of such an event.
– Say, you see something or someone, say X. How does that “seeing event” happen? What are the steps? What falls on the retina (at the back of your eye) is an upside-down image of X. How does the mind “see X”?
– If you really want to understand that, you need to read the subsection: “Citta and Cetasika“.
You can ask questions from those posts, if you really want to understand the details. But those details are not needed to make progress on the Path.
– What is critical is to avoid dasa akusala or immoral deeds (miccha ditthi being the most important), and to cultivate kusala (moral deeds).