The difference between 4 sentences, Thanks

[Gёггч]

Hi:
Can i say
what the only one thing i don't know is your name
Or
the only one thing which i don't know is what your name is

[2006]

Originally Posted by Gёггч

Hi:
Can i say
what the only one thing i don't know is your name
Or
the only one thing which i don't know is what your name is

All you need to say is, 'The only thing I don't know is your name.'

In the first sentence, using "what' is wrong and you don't need "one".
The second sentnce is much too wordy. (too many words)