The work done is 100% remote in all cases, and the employee does not care at all where the employee does his/her work. For examples sake we can assume that the work in question is programming, although in the real world case it can be a variety of other things too.
The company is located in Ireland. The employees can be located anywhere, though EU area would be the most immediate practical case. The employees might or might not be citizens of the countries they're residents in.
The employee is an actual employee (yet the company does not care at all about their physical location). Which country's employment laws apply?
The employee is actually not an employee but a contractor with a contract for service with the company. Let's say there's some dispute regarding his/her employment status. Which country's employment laws apply?