Hi, this must be a tricky ones even for the guys at Episerver :).
Have you tried using SearchClient.Instance.Statistics().GetSpellcheck(myQuery) ?
As Per Magne stated the Spellchecker is still availible in the api/Rest api but as of now not in the Find UI (i.e you can add editorial suggestions through the api but not through the Find UI).
Has the Spelling Suggestions been removed from FIND 11? I would like to have a Spelling Suggestion on my search results page but I cant seem to find out how this is implemented in Episerver FIND 11 (CMS 9).