Hi,
What do you mean by "template layout" ?
In the settings of the "Redirect Joomla registration to HikaShop plugin" in the Joomla plugins manager, you have a setting where you can enter the id of a menu item to use for the registration form of HikaShop.
Ideally, you want to create a menu item of the type "HikaShop user registration form" and enter the id of that menu item in this setting so that the HikaShop registration form will use that specific menu item.
Once done, in that menu item, you can select the template to use for the rendering.