What is the correct temperature probe for a wet etch solution? What type of probe or probe coating should one use to measure the temperature of a roughly 100c aqueous solution of cupric chloride?

A stainless steel probe seems incorrect. Is a Teflon coated probe sufficient or is something else more appropriate?

Is there a standard way of protecting metal probes in corrosive liquids?
Teflon is resistant against corrosive chemicals and stable up to temperatures of about 200 °C, so it is suitable for use in hot aqueous salt solutions. Using a coating or casing made of plastic which is unreactive and resistant against heat should be a good way to protect temperature probes.