Does Samira W Block Blitz Hook?

Samira's W will block all projectiles that enter or are in the vicinity of her W when it's active. This means auto-attacks, skill shots, and most importantly, CC like Hooks or knockups (like Nautilus Ultimate).

Does JHIN W go through Samira W?

According to the wiki page on projectiles, Jhin W is the only ability that interacts differently between Yasuo and Samira.

Can Samira block Gragas ULT?

She also doesn't block Gragas's ult properly.