Is the sum of 2 numbers in list k I got a coding problem to solve and was wondering if I got a commonly acceptable and efficient/clean solution. If there is a better way I'd gladly hear it. 


  given a list with numbers return if the sum of 2 elements in the list = k


def is_sum_of_2nums_in_list_k(list, k):
    for i in list:
        if k - i in list:
            return True
    return False


They also mentioned you get bonus points if you do it in one 'pass'. What does this mean?
You are using one explicit pass over the list (for i in list), and one implicit pass over the list (k - i in list).  This means your algorithm is \$O(N^2)\$.

Note: You can reduce your implementation to one line:

return any(k - i in list for i in list)


But you have a bug.   is_sum_of_2nums_in_list_k([5], 10) returns True.

A one pass algorithm


starts with an empty set,
takes each number in the list, 


tests if k-i is in the set,


return true if it is,

adds i to the set. 

returns false