Customise Screen Query

Hi,

We're looking to add a field to the 'Create Task' Screen located in Administration > Advanced Customisation > Workflow > New > 'Create Task'.

To show what we're after, I've amended the page code via the Chrome Browser.

See image below for specific screen;

I assume this is a page that's not normally edited so I've not been able to locate the screen via 'Customisation' > (entity name). I've searched through every entity but been unsuccessful in locating the right screen.

I can only assume this is an asp page that needs editing? Does anyone know how to locate this screen?

Thanks,

Will