Actually, each of those 所 belongs to something different, but all very similar. I will break that last part up for you, as it does not really pertain much to the original meaning of the word. 来中国后所见所闻所思所想 * 所見所聞 is an idiom which means "what one hears and sees" *所思 means "what one thinks" *所想 refers to "what one considers" or essentially, one's thoughts. So that last topic is basically asking you to consider what you would hear, see, think, your thoughts after arriving in China.

所见=what you saw 所闻=what you heard "所+verb."=what you +verb.( usually past tense). it is just like a noun. for example 所思所想what you think about/you are thinking about 所作所为=what you did sometimes we add的after the verb. 你所写的=what you wrote 你所吃的=what you ate 你所希望的=what you hoped or you can also add the object of the verb to make it clearer. 你所写的字=the words that you wrote 你所吃的饭=the food that you eat 你所救的动物=the animals that you saved.

所：所有的意思。 所见:看到 所闻：听到 所想：想法 所思：思想 所见所闻：所有看见和听见的

it's a part of separate words 所见 = seen (something that was seen) 所闻 = heard (smth that was heard) 所思 = thought (smth that was thought) 所想 = wanted (smth that was wanted) the secrets of Chinese word-building :P