I would like to make Nigella's Chocolate Guinness Cake but should I use the draught Guinness can or the original can type that is in the shops?
Guinness is sold in two forms. The original Guinness in cans and bottles and a draught Guinness in cans (and sometimes in bottles). The main difference between the two is the process used in actually canning the Guinness in the first place. The draught form uses a special plastic gadget - called a "widget" - and nitrogen gas in the can to help to agitate the Guinness when the can is opened. This results in smaller bubbles of gas in the Guinness and leads to a creamier "head" on the Guinness when it is poured, giving a glass of Guinness which is much closer to a draught pint poured in a bar.
This process may help when drinking Guinness but it doesn't make much difference if cooking with Guinness. So you can use whichever form of Guinness you prefer, or have available, for all of Nigella's recipes using Guinness.