To be sure you are earning interest make sure that it has a lockTime field set.
1. search the transaction using http://kmd.explorer.supernet.org/ .
2. search the transaction ID in the explorer and in the first section at the bottom will be lockTime.
3. check if it has lock time setup. (if it doesn't then it means you are not earning any interest).
4. if yes, then the address where the tx was sent to is acquiring interest.
Note! If locktime is set and it is for more than 10 KMD, interest is accruing
so as long as the wallet you use implements the spending of interest, you are fine.