Hello Micey123,
I think the link provided went to a phenomenal post, but there may have been a misunderstanding about what the post was instructing. From what I could tell, it was about tracking your own internal site predictive search, and not Google's.
Assuming you can get the full referrer path, including query string, in GA or via log files, I think one way to approach it would be to separate the queries from last to first, and you'll see the last is probably the original query that was "assisted" (or "interrupted", depending on how you look at it) and the first one in the URL was the auto-complete suggestion that was chosen. Here are a few examples.
This is the URL from my address bar while searching on Google for “I’m searching for something" without quotes, and selecting the suggestion for "I'm searching for something".
First query in the URL string (I'm searching for something):
q=i%27m+searching+for+something
(q=i%27m = I’m)
Second query in the URL string (I'm searching for):
q=i%27m+searching+for
This is the URL from my address bar while searching for “baby pandas are” without quotes, and selecting the autocomplete suggestion for “baby pandas are ugly”. I agree Google. Hideous creatures.
First query in the URL string:
q=baby+pandas+are+ugly
Second query in the URL string:
q=baby+pandas+are
URL from address bar while searching for “typing in full” and selecting the autocomplete suggestion for “typing in full sentences”.
Same pattern.
This is the first…
day of my life lyrics (after “day of my life”).
First query:
this is the first day of my life lyrics
Second query:
this is the first day of my life
I hope this helps. But there may be an easier way. I'll will ask around for you if you'd like, but I want to make sure I understand your needs first. Do I?