can a bsc.geography student take data science in pg
Yes, for sure! Most of the Data Science course in Post Graduation does not require a very heavy CS background. What they require is that how is your general aptitude and how strong is your mathematics background. So, if your maths is strong (linear algebra, calculus, probability, statistics etc.), there won't be a problem and you can easily switch your stream.
Hope I have answered your question. All the best!