Where am I supposed to place this code?

You could put that in the Resources of the xamSchedule control, one of its ancestors or even in the Application's Resources.

I use that code so it has error : Type 'igPrim:ClickToAddActivityElement' was not found. 

And I not see any type 'igPrim:ClickToAddActivityElement'  in file "generic.shared.xaml".

Have I got some wrong?

Well in the generic.shared.xaml it would not be referred to as igPrim:ClickToAddActivityElement since the URI syntax does not work on the local assembly so when we write the xaml that is embedded in our assembly we have to use a different prefix. If you just search for ClickToAddActivityElement then you will find it.

I see that : When I add  Appointments by hide code then Click to Add Appointment not be disabled.

What I do to disabled this dialog in this case. 

Thanks for help.

it is OK, thanks for help.

The ClickToAddActivityElement has nothing to do with the dialog; that simply relates to the "Click to Add Appointment" prompt that is displayed within a timeslot when you hover over it. If you don't want users to add using the activity dialog (i.e. what you see when you double click on a timeslot) then you can handle the ActivityDialogDisplaying event and set e.Cancel to true as needed (e.g. if the DataItem is null). If you are using 11.1 then you can set the IsAddViaDoubleClickEnabled on the ScheduleSettings->AppointmentSettings to false.

I implement to add some Appoiments by hide code.  For dont want users add Appoiments by 

Dialog I  add:

<Style TargetType="igPrim:ClickToAddActivityElement">
 <Setter Property="Opacity" Value="0" />
 <Setter Property="IsHitTestVisible" Value="False" />
</Style>

So I see that, it still allow user add Appoiments by Dialog.

I'm sorry but I don't understand the issue you are having. Can you provide a sample that demonstrates the issue and steps when running the sample? Or perhaps provide a more detailed description with screenshots?