For the people who cross it frequently one crossing of the Atlantic is very much like another.

For the people 状语
who cross it frequently 定语,修饰people
one 主语
crossing of the Atlantic 定语,修饰one
is 谓语
very much 状语,修饰like
like another表语

For the people who cross it frequently one crossing of the Atlantic is very much like another.
在该句中,one crossing 是主语,of the Atlantic 做one crossing 的定语,is是连系动词,也可以称之为系语,very much like another放在be动词之后,可统称为表语,也可以理解为like another是表语,very much 做状语修饰like another.“is very much like another”是系语和表语结合起来,也可统称为谓语.
For the people who cross it frequently作状语,其中,people是中心词,who cross it frequently是定语从句,做的是people的定语,在定语从句中,who是从句中的主语,cross是从句中的位于动词,it是做cross的宾语,.frequently做的是定语从句中的状语.