By default every user that can use Worklog PRO. But administrators may restrict the add-on to some group of users. Please check Permissions section of the add-on settings. Related permission is "Limit Groups That Can Use WorkLogPRO" permission. If this value is empty (default), every user can use WorklogPRO (but this does not mean they can enter worklog or do other operations restricted with other permissions). If you select user groups, only users in selected groups can use WorklogPRO.