Can anyone tell me the right compost to plant a Cordyline in

Its' not fussy, but I'd choose John Innes, unless you need to move it around easily, in which case a good multi purpose compost. There is a rumour flying around that they need acid soil - they don't. They do not, though. like to dry out, and may need protection during the winter.

If in a pot use John Innes No 2. Put the pot in the correct place before filling with compost as it is heavy!