How do I summon a villager with a certain profession?
This can be accomplished in Bedrock Edition using spawn events. For example, you use the minecraft:spawn_librarian spawn event to summon a librarian villager:
/summon villager X Y Z minecraft:spawn_librarian
Spawn events also exist for farmers (minecraft:spawn_farmer), clerics (minecraft:spawn_cleric), armorers (minecraft:spawn_armorer), and butchers (minecraft:spawn_butcher). See Minecraft Wiki for a complete list of spawn events.