Can 'whenever' abilities trigger multiple times per turn?
On the card it says you get a 6/6 dragon token whenever a dragon you control attacks.


  112.3c Triggered abilities have a trigger condition and an effect. They are written as “[Trigger condition], [effect],” and include (and
  usually begin with) the word “when,” “whenever,” or “at.” Whenever the
  trigger event occurs, the ability is put on the stack the next time a
  player would receive priority and stays there until it’s countered, it
  resolves, or it otherwise leaves the stack. See rule 603, “Handling
  Triggered Abilities.”


So every time the trigger event occurs. But you can't activate abilities when attackers are being declared.


  603.2a Because they aren’t cast or activated, triggered abilities can trigger even when it isn’t legal to cast spells and activate
  abilities. Effects that preclude abilities from being activated don’t
  affect them.


There are two types of abilities (that use the stack): activated abilities (which can also be loyalty abilities) and trigger abilities. Trigger abilities can trigger whenever; hence the word whenever/when.


  603.2c An ability triggers only once each time its trigger event occurs. However, it can trigger repeatedly if one event contains
  multiple occurrences. Example: A permanent has an ability whose
  trigger condition reads, “Whenever a land is put into a graveyard from
  the battlefield, . . . .” If someone casts a spell that destroys all
  lands, the ability will trigger once for each land put into the
  graveyard during the spell’s resolution.


For every occurrence. Even if no one can react between those occurrences.

So you get as many dragons as you attack with.