What restrictions are on there on this response

"Kneel IS to cancel an effect that would move a card out of a player's dead or discard pile"

Does this work when more than one card is being moved or is it applicable to effects that only move one card?

It is applicable to effects that would move multiple cards at the same time. Compare to those Stark effects that say "cancel an effect that would choose a Stark character as the ONLY target"; when the effect is hard-line about "just one," they make it clear.