For the name of person, there are many kanji which are read irregularly. When we don't know how to read, we can ask if we are together in person. However, the ones which we don't know in person, we have to search how to read if you want to know. You can find easily the name of the famous people on internet if you copy and paste on Google or something. I hope this was helpful. If you still have doubt, please let me know.

Thanks Kennan, 大 is thankfully one of the kanji I do know at least two pronunciations of c:

Kanji always have at least 2 ways to read. One with hiragana and one with not. For example, sorry i cant type Kanji on my mobile, therer is a ward means big. With hiragana, u would read it as o ki i but if there is no hiragana next to it, u would read it as da i. but there are so many cases that have 2 or more way to read when it does not come with hiragana so you need to check way to read