On a training contract/vacation scheme application, should I write my work experience in prose or bullet points?

Whilst either method is fine, here’s what’s adivsable:

For a CV - bullet points.

In a work experience section on an application form - prose.

By writing in bullet points on a CV, you’re following the standard way CVs are set out.

Alternatively, if you write your work experience in prose (i.e. full sentences) on an application form, you’re giving recruiters another opportunity to see how you write/express yourself.