Answer: Metaphysical skepticism
Step-by-step explanation:
Metaphysical skepticism is defined as the process in which a person tends to doubt or deny knowledge based on actual component like mind, component, nature reality, believes of reality apart from physical environment etc and the understanding one persist for it.Metaphysical data and facts are considered non- reliable till established proof are not present for it.
According to the question, Robert is displaying metaphysical skepticism by doubting or not being sure about the metaphysical knowledge of existence of objective moral goodness and related facts .