How to test the value of an attribute with a complex name?

I need to test the value of an attribute with a complex name which includes some kind of schema qualification.

Here’s the response body I’m testing:

{
    "urn:ietf:params:scim:schemas:extension:enterprise:2.0:User": {
        "costCenter": "123"
    },

I don’t know how to specify the costCenter attribute in the test. Here’s one of the things I’ve tried so far:

Unfortunately this syntax doesn’t work.

pm.expect(pm.response.json().urn:ietf:params:scim:schemas:extension:enterprise:2.0:User.costCenter).to.eql('TestCostCentre1');

Nor does this:

pm.expect(pm.response.json()."urn:ietf:params:scim:schemas:extension:enterprise:2.0:User".costCenter).to.eql('TestCostCentre1');

Any ideas much appreciated!