should

should /ˈʃʊd/ /ʃəd/ verb
should
/ˈʃʊd/ /ʃəd/
verb
Britannica Dictionary definition of SHOULD
past tense of shall
[modal verb]
1 
a  — used to say or suggest that something is the proper, reasonable, or best thing to do
b  — used with have to say that something was the proper, reasonable, or best thing to do but was not done
c  — used with have to say that you wish someone had seen, heard, or experienced something
2 
— used to ask for someone's opinion
3 
— used to say that something is expected or correct
4 
a  — used when saying that you feel a specified way about someone's words or behavior
b  — used to emphasize what you believe, think, hope, etc.
5 
— used with have in negative statements as a polite way of thanking someone for doing something
6 
somewhat formal — used to talk about the result or effect of something that may happen or be true
— usually used with if
7 
British — used to say that you would do or feel something if something specified happened — only used after I or we
8 
British — used when giving someone advice — only used after I or we
9 
British — used to say that you want to do or want to have something — only used after I or we

how/why should I/we know

— used to say that you do not know the answer to a question and are surprised that you were asked it

what/who should you see but

— used to say that you are surprised to see something or someone