Learn Icelandic: Ertu til í samskotaveisluna okkar í kvöld?

The idiomatic phrase vera til í (to be up for) is driven by the preposition í, which governs the accusative case in this context. Therefore, the noun becomes samskotaveisluna instead of the nominative samskotaveislan.

What exactly is a samskotaveisla?

It is a compound of samskot (a collection, contribution, or chipping in) and veisla (a party or feast). It perfectly translates the concept of a potluck, where everyone brings something to share.

Why does the sentence say samskotaveisluna okkar with the definite article on the noun?

In Icelandic, when you use a possessive pronoun like okkar (our), the preceding noun almost always takes the definite article suffix. Literally, it translates to "the-potluck our". Note that okkar is simply the genitive of við (we) and never changes its form to match the noun.

How would I change this to ask if someone is up for doing an action?

When using vera til í with an action rather than a noun, you add the infinitive marker að followed by the verb in its infinitive form. For example, Ertu til í að koma í kvöld? means "Are you up for coming tonight?"