Learn Hardcore Icelandic: Ég spila tónlist.

Icelandic doesn’t use a separate indefinite article like English a or an. Indefinite singular feminine nouns in the nominative (like tónlist) simply stand alone. If you wanted the music, you’d add a definite ending: tónlistin.

What case is tónlist in, and why doesn’t it change form?

Here tónlist is the direct object in the accusative case. Many feminine nouns (especially -ut ending compounds) have the same form in nominative and accusative singular. So tónlist remains unchanged whether it’s the subject or object.

How do you pronounce ég and the final g?

é is pronounced [jɛː], similar to English “yeh.”
The final g is a voiced velar fricative [ɣ], not a hard [g].
Altogether ég sounds roughly like [jɛːɣ].

Why is the verb spila right after ég? Doesn’t Icelandic have V2 word order?

Icelandic main clauses follow V2: the finite verb must be second. Here the subject ég occupies position one, so the verb spila comes second, and the object follows. If you front another element (like an adverb), spila still stays in second place:
“Í dag spila ég tónlist.” (Today play I music.)

Can I drop the subject and just say ?