Expenses per organisation

The organization is not an information of expenses.
Do you mean per projects of a given organization ?
Just define a filter for projects, to get all projects of an organization (may be dynamic).
Then on project selector, use the search option, apply filter on organization, select all project : then the selector applies to the filter youi wish.
You can go to Expense screen, you get the information you wish.
Interest is that this can be applied to any screen, not only expense (and get for instance Risks per organization),
and to any filter on Project (Expenses per type of project, or Situation of project).
 

We can extracts costs, via the reports in csv, per ressource, per period and per organisation.

You can get costs per organization as costs are linked to resources that are linked to organizations.

no I wanted to say, independently of the link project - organization
...
My request was just to have something similar for the expenses, in particular the table expenses per organisation. Regards.

No, not independently to link project - organization, as expenses are not directly linked to organization, nor to resource (except for individual expenses)

The only way to do what you expect is to use the plugin Screen Customization.
With this plugin, you can easily add new field idOrganization to Project Expenses, then you'll be able to use this field on your reports.