Most lawyers in cases like this are not assholes (surprisingly), so they generally won't spend time/energy deposing people who can't produce useful evidence, even if they could.
As a result, you would generally stick to people who have relevant evidence, are capable of legally binding the company (often director or above) or speaking for it (various others), etc.
But - if you need to prove a coordinated campaign, and can't get evidence of it otherwise (emails, chats, etc), sometimes you just got to depose a lot of people.
Usually the path of least resistance is taken, however, and electronic evidence is often sufficient enough these days to not end up having to depose lots of employees.
Judges (magistrate and otherwise) also are pretty careful in ensuring you aren't being malicious (IE just trying to harass employees)
Most lawyers in cases like this are not assholes (surprisingly), so they generally won't spend time/energy deposing people who can't produce useful evidence, even if they could.
As a result, you would generally stick to people who have relevant evidence, are capable of legally binding the company (often director or above) or speaking for it (various others), etc.
But - if you need to prove a coordinated campaign, and can't get evidence of it otherwise (emails, chats, etc), sometimes you just got to depose a lot of people.
Usually the path of least resistance is taken, however, and electronic evidence is often sufficient enough these days to not end up having to depose lots of employees. Judges (magistrate and otherwise) also are pretty careful in ensuring you aren't being malicious (IE just trying to harass employees)