When Welder is used to attach 2 Fire energy, does Old Cemetery trigger once or twice?
Any energies attached from the hand would trigger Old Cemetery, once for each energy card being attached. So in this case you would put 4 damage counters total.
Source: TPCi Rules Team (2022-01-20)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH6_147
SWSH6_147
SM10_189
SM10_189