There are 4 cases when you may have this question:
1) when you upload a list of keywords using CSV;
2) when you add keywords from one adgroup to another;
3) when you add search terms as keywords to another adgroup;
4) when you add keywords from Keyword Planner to your adgroups.
The general rule is if you try to upload the same keywords into the same group you will see an error message and SearchAdsHQ will not allow you to add duplicates to the same adgroup. However, you can add them to different groups, so you need to be careful with this so that you do not have the same keywords across multiple adgroups. In the future, we will improve the deduplication mechanism to prevent this, for right now please bear this in mind.
When you try to add them, you will get an error message. You can download an error report from here to see what keywords are duplicates. Tick "add only keywords without errors" in order to add the keywords.