How do you attach a plaque to a brick wall with screws?

Hi, morvis!

Using lead screw anchors would be one, possible option.

Lead Screw Anchors - Google Search

There are also specific masonry anchors that could be used that would probably be better than using the lead ones.

Masonry Screw Anchors - Google Search

Masonry Screw Anchors - Google Image Search

Clough is on the right track, I'd use a tapcon.

Buildex Tapcon®

The first posts were correct but I am wondering if you plan to have this plaque on the wall for all time? If only for a few years you might want to glue a piece of pressure treated plywood to the wall with exterior construction glue and then screw into the ply. If you ever want to take it down it will still be a chore to dissolve the glue but no wholes.

You might consider installing fastener in Grout line, it can be repaired in the future.