i have jcobs flor pfac tyo jgc SAMSUNG found most standards same. so advice to go through basics standrds and specification not specific company standards.

as per my view following things learn for c&i design engineer.
p&id .cause &effect diagram.loop scematics diagram.hook up.level skecthes.layout drawings,cable list/schedule/jbschedule.logic diagram. .technical bid analysis ,and dc/plc documents thats all about instrumentaion & control enginnering person who worked ion epc companies for person working in plant basic maintenance practice.