Let us develop a checklist for clause 7.2 of ISO 14001:2015 and hope you can apply the same technique to develop a checklist for any clause of ISO 14001:2015.
Translate clause 7.2 into a set of actions, look for the verbs:
a) determine the necessary competence of person(s)
b) ensure that these persons are competent
c) determine training needs
d) take actions to acquire the necessary competence,
d) evaluate the effectiveness of the actions taken.
Now, where do you want to start your audit? At the end? In the beginning? In the middle? Let us start at the middle.
Have you determined training needs? (about c)) Did you plan actions to address them? Can I see your overall plan to address them? (about the first d)) Was the plan approved? By whom? Was the plan fulfilled? Choose two or three actions and ask for evidence of their realization. Who participated in these actions? Why? To what extent have these actions met training needs? Has the effectiveness of these actions been assessed? What was the result? Can I see evidence of the evaluation? (about the second d)) To what extent have these actions met skills gaps? Can I see those gaps? Choose two or three people who attended the chosen training courses and see what are the competence requirements of the functions they perform (about a) and b)) and how did the training contribute to their evolution?
Translate the standard into verbs, then ask questions to check if the actions were done and evidence of that.