Unfortunately, the current version of AEM 6.0 does not support the spellcheck feature. I learned this the hard way. From my understanding, AEM 6.0 SP2 still uses OAK 1.0.9. Spellcheck support in OAK has being added in 1.1.0
But here the information on how to at least enable SolR search in AEM 6.0 (which is still better than the normal JCR search) and you should be ready for the spellcheck support when it happens
To enable the spellcheck in SolR you can look at the SolR Spellchecker documentation
If my understanding is correct, OAK 1.1 should use the SolR spellcheck if it is there.