First, check whether your transaction executed successfully using a blockchain explorer like https://etherscan.io/ or https://etherchain.org/.
If your account balance includes the transfer, then it is most likely a problem with the syncing of your blockchain data, as @eth's mentions.
If it is a syncing problem, and your computer runs on a hard disk drive (HDD) and not a solid state drive (SSD), the reason for your syncing problem is due to the recent attacks on the Ethereum network. The attacker sent many many low cost transactions that caused the blockchain node clients to slow down, and the hardest hit are clients running on HDD drives.
The solution if you have a HDD drive is to either upgrade your computer to a SSD drive, or wait until the next hard fork when the node clients will attempt to remove some of the data that slows down syncing. The latest update on the upcoming hard fork can be found at [UPDATE] Hard Fork Block Number Delay [10/31/2016].
If you have a SSD and more than 4 Gb RAM on your computer, clear out your old blockchain data by deleting the chaindata directory on your computer, or finding the geth executable and executing geth removedb to remove the old chain data. Then run Mist and it will attempt to sync again.
The default chaindata directory can be found in:
- Mac:
~/Library/Ethereum
- Linux:
~/.ethereum
- Windows:
%APPDATA%/Ethereum
(Remember not to delete your keystore directory as this directory contains your private keys).
All of this assumes that you have the latest 0.8.7 Mist (or Ethereum Wallet).
About your first question: Etherscan is a search engine, not an exchange. You cannot sell ETH there, only look things up.
About your second question: What Ethereum address did you give when you purchased from Bitpanda? Normally, that's when you would have entered your Ethereum wallet address at Coinbase. Here is a short primer on how this typically works. By the way if you are using Coinbase for storage, you might want to read this post and that post about how to safely store your Ethers.
Best Answer
Technically you're not sending it to your Mist wallet. You're sending it to another Ethereum address. Mist just helps you create accounts/addresses that are recognized by the Ethereum node that's embedded in Mist.
I have not used coinbase to send Ether. But I assume that coinbase provides some kind of a form to send Ether. In that form, you want to specify the address you want to send Ether to. That address should be one that you have in Mist.
NOTE: Before you hit the send button, double and triple check the address you are sending TO. If you send to the wrong address you've lost that money forever