A "hard" science?
A general liberal arts degree?
Accept the past. Live for the present. Look forward to the future. Robot Fusion
"As our island of knowledge grows, so does the shore of our ignorance." John Wheeler
"[A] scientist looking at nonscientific problems is just as dumb as the next guy." Richard Feynman
"[P]etabytes of  data is not the same thing as understanding emergent mechanisms and structures." Jim Crutchfield
The scenarios you encounter and are forced to consider branch every field you can think of from ethics, to psychology, to sociology, to biology, to economics, etc. Your ability to see past propaganda and fallacies is essential to your success in obtaining correct information and utilizing it to the benefit of your client. Failure to do so can have weighty consequences, everything from unwanted pregnancies, to suicide or homicide. I know an experienced ICU doctor who says he could not stand to make the decisions everyday that a child welfare social worker has to make based solely on police reports and parent's testimony.
Not to mention that the topic of critical thinking is found in the first chapter of every Introduction to Social Work text I have encountered.
Philosophy, though I tend to think that Religious studies does a better job of bringing culture into the mix.
"I can never be what I ought to be until you are what you ought to be. You can never be what you ought to be until I am what I ought to be. This is the interrelated structure of reality." -Martin Luther King, Jr.
Actually, not necessarily straight philosophy, which I think can foster memorization more than critical thinking -- my answer is critical theory. Yes, critical theory is a subset of philosophy but it it's also a subset of many other fields. It can be found in comparitive literature, general art criticism, different offshoots of philosophy (say where you have to break down sexuality and gender, economic models and their actual impact on living standards) and liberal arts colleges in general.
To take the tools or bones of a theoretical system and apply it to something it wasn't necessarily meant for or objects where meaning has to be extrapolated and interpreted, that's at the heart of...a kind of critical thinking?
I personally think true art criticism, taking a work and fully breaking it down internally to its bones and externally to its larger context -- is a real test of critical thinking as well as of course specific & general knowledge (about art movements, historical events, artists, etc.) and understanding of concepts & theories (what the style of the piece is trying to achieve, what is the audience-object relationships, etc.). A lot of people think it's fluff because by nature anything 'open-ended' is easy to fake an answer to, but to really do a piece justice, it takes a penetrating gaze and multi-faceted thinking.
I also think jurisprudence takes critical thinking skills, albeit in a much more strict, linear, closed system kinda way. It's kinda frustrating that way.
“If you want to tell people the truth, make them laugh, otherwise they'll kill you.” ― Oscar Wilde
A psychologist can think critically about human motivation and the mind. A philosopher MIGHT, but a philosopher would be better skilled at taking apart arguments. An attorney might be good at sorting out duties and responsibilities but horrible in domains of human motivation outside of business. Etc, etc.
No specific curriculum... any field of study which requires you to do independent thinking rather than memorization of information (and this include mathematics and the so call "hard" physical sciences where you memorize the method of calculating/solving something).
Philosophy wins for challenging beliefs and perspectives, to the point of challenging how you challenge beliefs and perspectives. (And then challenging how you're challenging the challenges of those beliefs and perspectives...)
Mathematics comes in second for destroying your mind.
And I will debate this with every philosophy major until I die, but I still think mathematics is unarguably the most rigorous discipline. But that doesn't necessarily translate into critical thinking skills.
You can't wait for inspiration. You have to go after it with a club. - Jack London