Ég á níu penna.

á is the 1st person singular present of eiga, which is the standard Icelandic verb for “to own” or “to possess.”

• English uses a single verb “have,” but Icelandic normally uses eiga to express possession.
• The verb hafa does exist (meaning “to hold,” “to contain,” or in certain idiomatic/fomal contexts), but it’s not used for everyday ownership.

Icelandic numerals govern the form of the noun that follows:

• Numerals 2–4 take the nominative plural (so “two pens” = tveir pennar).
• Numeral 1 takes the nominative singular (so “one pen” = einn penni).
• Numerals 5 and above take the genitive plural, regardless of syntactic case. Since níu (9) is ≥ 5, penni becomes penna.

Icelandic has no separate indefinite article (“a/an”); indefiniteness is unmarked. For the definite you add a suffix:

• penni = “a pen”
• penninn = “the pen” (singular)
• pennarnir = “the pens” (plural)
  With a numeral you never add the definite suffix, so you simply have níu penna for “nine (unspecified) pens.”

Icelandic main clauses follow the V2 rule: the finite verb must be in second position.

• Standard SVO: Ég á níu penna.
• To emphasize “nine pens,” you can front that phrase: Níu penna á ég. (“Nine pens I have.”)

You say Hvað áttu marga penna?

• hvað = “what/how many”
• áttu = 2nd person singular of eiga (“you have/own”)
• marga = accusative plural of margur (“many”) to agree with the noun
• penna = genitive plural of penni (required by numerals ≥ 5)

For numerals 2–4, both numeral and noun appear in nominative plural, even as an object:

• Ég á þrír pennar.
  • þrír = masculine nominative plural of “three”
  • pennar = nominative plural of penni
  This stays the form whether it’s subject or object—accusative is overridden by the numeral.