It is important to gauge team’s sentiments, to know how happy they are with current work. To understand this, it is required to capture this through some metrics. There is one metrics to capture this, called happiness metrics.
Where to capture
The right time to capture this metric is at the time of retro. Scrum Master can capture this metrics with the help of any of the tool like MS forms or some other survey. May be in some shared space also. Basically the idea is to capture sentiments through various questions. The question can be like below :-
How to feel you about this sprint ?
Are you happy with your work ?
Are you happy with your team ?
How management can help you to be more productive ? etc.
What to do with this metrics ?
Capture this metrics sprint on sprint. See the trends how it coming ? What are the common sentiments. For Scrum Master it is important to track these trends and take some action on them.