Step 1. Open the GRASS Mapset which contains your lidar (raster) grid data (as above).
Step 4. When we open the attribute table there is a new 'value' field containing the height values which we can now query. On the bottom right of the attribute table click 'Advanced Search' (below) using the query: value >= '28' AND value <= '53' then click 'Test' to verify the query structure works. The Search has found 2178 matching features, Click 'OK' (search results) and 'OK' again on the query builder.
Step 5. We can now see the results highlighted in amber.