I was thinking about studying this awesome science but, unfortunately, it's not being taught anywhere in my country (Czechia). What is the closest scientific branch to cognitive sciences?
As @Lucianopaz said in his answer, this question is very broad and depends on what area of Cognitive Science you are interested in.
As the link I provided says, there are 6 main sciences within the collection;
- AI (Artificial Intelligence)
but within those sciences there are branches.
Take Psychology for example, and you could specialise in Social Psychology, Behavioural Psychology, Criminal Psychology... the list goes on.
You need to work out what interests you within this collection of sciences to work out what you want to study in college and university.
I think it depends on what you find particularly interesting in cognitive sciences.
I think that if you are drawn to learn about human behaviour, emotion, learning, and other aspects of human cognition on an abstract level, then Psychology may be the best branch for you.
If you are interested in the neural-side of the matter, i.e. how a bunch of cells can organize and give rise to function, then you have a broad set of branches to look at. Biology is the most thematically related, and it studies the brain at several scales, from molecular biology that aims to understand gene-expression/regulation, the involvement of different proteins, neurotransmitors or other compounds in brain function, to ethology that studies how living organisms behave.
There are also other scientific branches that are becoming more involved in neuroscience such as computer-science, mathematics and physics, however the core of these branches is farther away from cognitive science than Biology and Psychology. Again, your question is mainly opinion based and it strongly depends on your particular inclinations.