Does Ezreal Prodigy reduce Death from Above cost?

No, Ezreal, Prodigy does not reduce the cost of playing Death from Below from your trash.

According to the RiftJudge FAQ #10246, Ezreal, Prodigy’s ability only reduces optional additional costs. These costs must be specifically identified by having both the text "as an additional cost" and the word "may" (for example, keywords like Accelerate and Repeat).

The ability on Death from Below ("You may play this from your trash...") is a recursive effect, not an optional additional cost. Because it does not contain the mandatory "as an additional cost" phrasing required to qualify for Ezreal's discount, you must pay the full costs as written on the card when playing it from the trash.