From:
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:ei="http://schemas.microsoft.com/expression/2010/interactions"
User : Source Object is your ViewModel.
<UserControl>
<i:Interaction.Triggers>
<i:EventTrigger SourceObject="{Binding}" EventName="YourEvent">
<ei:CallMethodAction MethodName="YourMethod"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</UserControl>
If you place it in a scope of another element then your view (UserControl) add
<ei:CallMethodAction MethodName="YourMethod" TargetObject="{Binding ElementName=yourUserControl}"/>