讷 as nò, an exclamation meaning "Here you go" Encountered this in the Pimsleur transcript:


  Nánrén: Wô gêi nî yìdiânr Rénmínbì. Nò.
  Shí jiû kuài Rénmínbì. Xiànzài nî yôu
  duöshâo qián?
  
  男人：我给你一点儿人民币。讷。 十九
  块人民币。现在你有多少钱？
  
  Man: I’ll give you some Renminbi. Here you
  go. 14 Renminbi. Now you have how much
  money?


They use it many times and always in the context of someone giving money or an item in a business transaction.  The translation is always "here you go" or "here you are".

I can't find any other uses of this word in this way, or any dictionary mentioning this meaning.  Is this a common expression?  Is it regional?

Is this the same thing as 喏 / nuò?
I think the correct character might be 

吶 na4 used as an auxiliary word 语助词

We say 吶 na4 sometimes when giving someone something, so saying 吶 + the gesture of giving the thing away does translate to "here you go". The way I have heard it the most is "呐，这个给你".

However, I'd only use 吶 in informal speech with family or friends. It's quite casual and I don't think it's appropriate for professional settings, including business transactions.


  Reference Notes



In the Zdic entry of 吶, it lists 讷 as interchangeable with 吶 when pronounced ne4 which means slow of speech or to speak with a stammer (讲话迟钝或口吃). I'm guessing this might be where typo stems from. 
From the same Zdic entry mentioned above, one of the meanings of 吶 is 表示提醒注意 to get someone's attention. I think this "getting attention" + "the gesture of handing over something" combined implies the meaning of "here you go".
As an auxiliary word 語助詞, you can use 吶 in other cases without the meaning "here you go", for example "天吶" equivalent to "天啊" which is an exclamation similar to "Gee" or "Yikes" or "Oh".
吶 is commonly seen as part of the word 吶喊 which means to shout / cry out.