The tab strip placement of the tabbed DockingWindows can be changed with the help of the following code :
[XAML]
<!--Bottom Tabbed -->
<DockPanel Name="DockingWindow1" Syncfusion:DockingManager.SideInDockedMode="Bottom"/ >
<!--Left Tabbed-->
<DockPanel Name="DockingWindow2" Syncfusion:DockingManager.SideInDockedMode="Left"/>
[C#]
//Bottom Tabbed
DockingManager.DockTabAlignment = Dock.Bottom;
//Left Tabbed
DockingManager.DockTabAlignment = Dock.Left;
Syncfusion Inc.