First, there is currently -- and until 4 January -- an exhibition at the Biblioteca Nacional of the Hours of Charles V, which was recently disbound for conservation:
About 30-40 leaves are on display, plus the binding and some flyleaves, with very good wall panels (in Spanish), covering the Iconography, the Artists, the Binding, the Conservation, etc., next to cases displaying relevant leaves:
It's probably not worth making a major detour, but if you're in Madrid before 4 January, it's worth taking a look.
Next is Luke, sitting at a similar desk, apparently writing left-handed, and holding his pen-knife in his right hand:
Mark keeps his exemplar open in the same way as John:
St Matthew is sharpening his quill: