For the card Get Excited, do you see what they discard before you can react or counter?

No, you do not see what your opponent is discarding before you have the opportunity to react or counter Get Excited!.

According to the RiftJudge FAQs for Get Excited!:

• Targeting: You must declare the targeted unit when you put Get Excited! on the chain.
• Reaction Window: Once the spell is on the chain, your opponent has the opportunity to react or counter it.
• Discard Timing: The discard is not a cost; it is part of the spell's resolution. You do not choose or reveal what you are discarding until the spell is resolving.

Because the discard happens during resolution, your opponent will not know how much damage Get Excited! will deal until after the window to react or counter has passed. If the spell is countered (e.g., by Defy or Windwall), it does not resolve, and therefore no discard occurs.