This pup is only 18 days old, she's the one I've picked to come home with me once she's old enough. Mom is short haired dachshund, father is long haired dachshund both minis.
I see lots of pups there lol. Could be either on the coat. My long haired guy came from a whole litter of smooth coats. I couldn't tell he was going to be long hair until he was a month or two old, and his ear hair looked "wavy" rather than completely smooth. That was my only indicator.
The attached pic is of mine, who is a long haired, when she was about 7 weeks. So although initially I was going to say this one will be a smooth for sure, after comparing the pics I'm not 100%.