There are three ways a request can be created with HelpDesk:
Customer Portal(s) – a special interface where you can set up the request creation form for your customers.
Email – receive new requests and comments by email.
Directly in Jira – a Jira user can raise a request on behalf of a customer directly in Jira as a usual issue.
Storing a request channel
To keep the information of the request source in an issue, follow the steps:
Create a custom field of the Select List (single) type for storing the channel. Add just one option – "Jira" or "internal" and make it default. The options for other channels will be added automatically while receiving requests from the Portal or from email (HD and E-mail cirrespondingly). Read: Configuring a custom field (Atlassian).
Add the field to screens if required.
Navigate to HelpDesk Settings → Customer Area → General Settings and select this field in the Source Field setting: