The most common and most likely answer to this crossword clue is the 8 letter word RAMBLING
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More clues leading to the result RAMBLING
Buddy explains!

The straight part
We know that "Going on and on" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case going on and on = rambling.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.
What does RAMBLING mean?
RAMBLING verb- To move about aimlessly, or on a winding course
- To walk for pleasure; to amble or saunter.
- To talk or write incessantly, unclearly, or incoherently, with many digressions.
- A long meandering talk with no specific topic or direction.
- A gentle hike.
- Of a speech: meandering, long and digressing.
- Confused and irregular; awkward.