I assume you are talking about Service Desk Customer Portal. Optional fields are marked as (optional). All other fields are required. You can add help line to each field in Customer Portal where you can emphasize that field is required with exlamation icon (!) + text or other formatting of your choice by using wiki markup.
Yep, this is for the service desk portal.
From what you are saying, Jira makes all fields mandatory as standard but doesnt put a marker against them to state they are mandatory. Is this correct?
Does that mean i need to type *Summary to show it is mandatory? Shouldnt there be a red astrix to show its mandatory? Why would my clients assume all fields are mandatory if they are not marked as so?