For multidoge from https://multidoge.org/help/v0.1/help_importASingleKey.html
You can import a single private key into MultiDoge that you have produced externally, perhaps by vanitygen or www.bitaddress.org.
The easiest way to get the format exactly right is:
Create a new wallet saved to a file, say, example.wallet.
Export the private keys, WITHOUT A PASSWORD, to a file example.key.
Open up the key file in a text editor. There is a big comment at the top that describes the format. It is simply lines, each line containing the sipa format key - beginning with 5 - and the key creation date in a particular format. You will have an example in there to copy as a new wallet has one key in it.
Add in your new key and a date a bit before when you created it.
Import the key file back into the wallet.
MultiDoge will then replay the blocks to get the transactions and work out the balance.
TIDY UP: It is good idea to then secure delete the key file so it is not lying around. If you want a quick key backup you can do another key export but add a password so that the key export file is encrypted.
Once you do that you can send the doge to wherever you want.
For mobile wallets, not all support importing / sweeping private keys. So those will require a bit more looking around for answers.
Although a lot of people do not like it, Coinomi does have a sweep function:
https://coinomi.freshdesk.com/support/solutions/articles/29000009716-migrating-from-other-wallets-into-coinomi
-Dave