Cut, copy, and paste work whenever your have a group, step, question, or variable selected: within flows, or even between flows.
However, if you are pasting content that depends on specific answers within the copied flow slice, such as variables used in a templated label, or a question that is conditional on another answer, you will be asked to map your flow's answers into the slice.
This will create a new question that asks the responder for the required answer, placed at the beginning of the pasted slice.
If you want to fix the answer mapping later, you can opt to create a placeholder answer.
Note that this will create an orphaned answer and therefore a non-publishable flow state, since no question will collect the answer when it is created. However, you will be able to create a new question that provides the required answer.
If you already have an answer collected within the flow that is of a compatible type to what the pasted slice requires, you can use that answer to complete the mapping.
This creates an external variable with a default value, which means that you will not need to ask the responder for an answer within the flow.