ouch!! I think you will need to do write a gliderecord query to intially go through sys_user and then for each user, look on those tables, I can think of 3 at least but there are bound to me more places, roles, group memberships, etc.

task - assigned_to

cmdb_ci - assigned_to

sysapproval_approver - approver

do a count where you find the user. an example to get started would be this to look for tasks assigned to the user

The script below would take a users sys_id and return how many tasks assigned to them

var task = new GlideAggregate('task');

task.addQuery('assigned_to', 'users sys_id');

task.addAggregate('COUNT');

task.query()

var tickets = 0;

if (task.next())

tickets = task.getAggregate('COUNT');

gs.print('this user has ' + tickets + ' tickets assigned to them');