We try to encourage people to answer the eNPS question at least once per month and, to achieve that, we have several ways:
Including the eNPS question as another question within the advanced metrics survey (this survey has an initial periodicity of 14 days).
Asking the eNPS question after sending claps.
Asking the eNPS question when they are looking at their position in the mood map.
Advanced metrics is a Pro feature, if you don't have access to them, the eNPS question will be sent once per month.