If my opponent attacked with Magby's "Scorching Heater" attack last turn and I evolve into Espathra with "Stance" Ability this turn, will my Espathra receive the 6 damage counters from "Scorching Heater" if it attacks and does damage to Magby?
No, it will not receive the 6 damage counters. Stance prevents all effects of your opponent's attacks, and Scorching Heater's damage counters are an effect of your opponent's attack.
Source: TPCi Rules Team (2023-11-09)

Relevant cards

Note: All applicable cards may not be listed below.
SV4_19
SV4_19
SV4_81
SV4_81