First here are a few tips to heighten your senses. Swirl the glass to release the aromas, but be warned, the high level of alcohol can numb the senses. We often dilute with water to help open up the aromas and to bring the whisky to a level where our noses can work at their optimum.
So how can we pick out one from another, just with a sniff!
First for the Single Malt from Scotland. You don't even need to put your nose in the glass to get a whiff of smokey peat. Laphroaig's peaty reek is particularly strong as they use the island's maritime peat to heat the furnaces in the malting houses, the hot smoke halts the germination and also imparts a wonderful peak reek. If you like the smell of lapsang souchong, bonfire smoke or tcp you will love this!
With Irish Whisky you won't generally have the smokey notes (Conemarra is a notable exception), as the malted grain is heated using coal fired closed kilns. I have Redbreast to show you, rich, plummy, spicy with a linseed, sherry edge from the sherry cask ageing, but not a whiff of peat smoke.
Last but not least, American Bourbon, made predominantly from sweet corn and by law has to be aged in new, toasted American oak. When the new spirit is made it is water white (show new pot), only with ageing in oak does it take on its golden colour and much of its flavour and aromas. This Woodford Reserve Bourbon has a perfumed nose, sweet, ripe banana, with a honeyed vanilla, spice from the new oak.