How doest hing works, do you discard dragons or do you have be discarded by stuff like card destruction or raigeki break?

1st the card...

Super Rejuvenation
Quick-Play Spell

During the End Phase of the turn this card is activated, draw 1 card for each Dragon-type monster discarded from your hand and/or offered as a tribute during this turn.

now the answer...
Since you can't just discard cards from your hand whenever you want, you need to activate a card that allows you to discard cards for a cost (Lightning Vortex, Divne Wrath, Grey Wing, etc.).

Hope that helps. :cool:

They have to be discarded from your hand/tributed by some outside effect.

What if you discard at the end phase, does that count too?

At some point in the End Phase, you would have to finish resolving "Super Rejuvenation"; if you discard the Dragon before, you would get it counted, if you discard the Dragon after, it obviously would not get counted.