I think I know what you are trying to say but I'm not exactly sure what you mean.
I kind of understand what you are talking about but not completely sure what you mean.
どちらも「言っていることはなんとなくわかるんだけど、完全に理解してるかどうかと言われればそうではない。」というニュアンスになります。
1) I think I know what you are trying to say but I'm not exactly sure what you mean.
I think I know what you are trying to say で「言おうとしていることはわかると思う」
exactly で「正確に・厳密に」
2) I kind of understand what you are talking about but not completely sure what you mean.
I kind of understand what you are talking about で「あなたの言っていることはなんとなくわかる」
completely で「完全に・完璧に」
ご参考になれば幸いです！
日本 
