what is the difference between ~는가봐, 는건가봐, -나봐, -구나/구먼?
Like 있는가봐, 있는건가봐, 있나봐, 있구나/있구먼?
Aren't they all expressing surprise?

Question

Answer

~봐:means that it seems like or it looks like
~는가봐, ~나봐: means it seems that someone or something do something. it may contains little surprising expressions depending on speakers nuance or accent.
~는건가봐:it is the past tense of above.
~나보다:means it looks like that someone or something do something.
~구나:means determining what someone or something did. 
~구먼?: it is a dialect in the south province of Korea. means "Did you or something do something?"

ご自宅で快適に語学を学べるチャンスをお見逃しなく。経験豊富な語学講師陣の中からお選びいただき、今すぐ最初のレッスンにお申し込みください！