Both pronunciations are used. It depends what comes before the phrase. 1. -(ㄴ/은/는) 것 같아 = [걷 까타]. (after an n sound, ㄱ pronounces normally) 2. -(ㄹ/을) 것 같아 = [껃 까타]. (after a ㄹ, ㄱ in 것 is pronounced like ㄲ) In daily conversation, however, we say the simplified 거 more often than 것, and this makes the last part pronounced as 가타 instead of 까타. That is, the ㅅ in 것 is what makes the subsequent consonant tensed, so if we use 거, it goes back to the normal sound 가.

There is something called "음절의 끝소리 규칙(Rule of ending sound of syllables)" and the ending sound of syllables should only be one of ㄱ,ㄴ,ㄷ,ㄹ,ㅁ,ㅂ,ㅇ. So 것 is pronounced as 걷 (ㅅ switched to ㄷ) Also about "같아", the second syllable has no consonant so the rule called "연음법칙(linking)" is applied. So it is pronounced as "가타" In conclusion its pronunciation is "걷 가타(gut gatta)"

것 가타 :)

It's pronounced as 'geot gatta'. Kind of like this: 걷 가따 [geot gatta]