Answer:
It really depends on the context. It can be ethos, pathos, or logos.
Example of logos in this argument:
"According to the FDA, the amount of chocolate you have been eating is unhealthy and can cause health problems later in life."
Example of pathos in this argument:
"If you were really a good brother, you'd stop eating all of that chocolate and give it to me!"
Example of ethos in this argument:
"As a sibling who is looking out for their brother, I need to tell you that eating chocolate is bad for you."
Really, it depends. Sorry if this is not the answer you are looking for.