If the effect of "DNA Surgery" is making all monsters on the field Dragon-Type, the ones that are Tributed will count for "Super Rejuvenation".
You can activate "Super Rejuvenation" at any time outside the Damage Step, and the effect will be applied during the End Phase.
Multiple copies of "Super Rejuvenation" are cumulative. So if you activate two copies during your Main Phase 1 and Tribute two Dragon-Type monsters during the course of the turn, you will draw 4 cards in the End Phase.
If you have "Solemn Wishes" active on the field, you can increase your Life Points by the number of cards you draw for the effect of "Super Rejuvenation" x 500. So if you drew 2 cards by its effect, you can increase your Life Points by 1000.