The most common and most likely answer to this crossword clue is the 9 plus 4 letter word AUXILIARY VERB
I've seen this crossword clue in The Times
A
U
X
I
L
I
A
R
Y
V
E
R
B
More clues leading to the result AUXILIARY VERB
Buddy explains!
The straight part
We know that "Will should have three examples of this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case will should have three examples of this = auxiliary verb.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.