While Tabernacle of Pendrell Vale is in play, permanent turned into Elk by Oko don't pay 1 extra during their upkeep or destroy the creature
Permanents turned into elk by Oko after a Tabernacle of Pendrell Vale is in play do not actually gain "Pay 1 during your upkeep or destroy this creature."
what if oko's 2nd ability was targeting an artifact (as opposed to a creature)? i mean, the way it is worded, the target artifact will lose abilities and become a creature - at which time, should then be subject to the tabernacle's continuous effect, no??
If the Tabernacle is already on the board when Oko Elks something, then the Elk won't have the upkeep trigger. The reason is that the ability gain and the ability removal happen in the same layer, and the Elkification has a more recent timestamp.
Now, if you have an Elk on the board and then drop Tabernacle, the Elk should end up with the ability.