If I have multiple V Guard Energy cards attached to a single Pokemon, will they each prevent 30 damage from my opponent's Pokemon V's attacks?
No, V Guard Energy does not stack. It specifically says on the card, "this effect can't be applied more than once at a time to the same Pokemon".
Source: Silver Tempest FAQ; TPCi Rules Team (2022-11-10)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH12_169
SWSH12_169