Which filter is used to get the top 10 values from a view?

A Top filter. On the Filters shelf, open the field's dialog, go to the Top tab, and set Top N by a field — for example, top 10 by `SUM(Sales)`.

It can rank by a field or by a formula, and a parameter can supply N so the reader can change it.

The subtlety worth raising is how it interacts with other filters. A top filter and a dimension filter are both dimension filters and evaluate together, so filtering to one region gives you the members that are in the overall top 10 *and* in that region — usually fewer than ten, and not the region's own top ten.

Putting the region filter in context fixes it, because the top N is then computed against the context table. That order-of-operations point is normally what the question is really testing.