The spelling of the name "Kittisak" is based on the phonetic sounds of its pronunciation. Using the International Phonetic Alphabet (IPA), we can break it down into individual sounds. "K" is pronounced as /k/, "i" is pronounced as /ɪ/, "t" is pronounced as /t/, "t" again is pronounced as /t/, "i" is pronounced as /ɪ/, "s" is pronounced as /s/, "a" is pronounced as /ə/, and "k" is pronounced as /k/. Therefore, the correct spelling of the name when following the sounds is "Kittisak."