VOLUME ONE: FANTINE

Just skip book 1 entirely
Book 2: most of it is good to read, tbh; you can skip chapter 8 if you want
Book 3: skip ch 1 and ch 4, 5 and 7 and 8
Book 4: read all of it
Book 5: read all of it
Book 6: read all of it
Book 7: read all of it
Book 8: read all of it

VOLUME TWO: COSETTE

Book 1: Skip all EXCEPT the very end, start from the last page or so, where it begins with XIX, The Battlefield At Night -- even then, it's just the last two pages and so which are the most important.
Book 2: Read the first paragraph, skip the rest
Book 3: Read all
Book 4: Skip the first chapter, read the rest
Book 5: Read all
Book 6: Skip
Book 7: Read all

VOLUME THREE: MARIUS

Book 1: Fine to read, but only the last chapter is relevant
Book 2: Again, fine to read, but only the last chapter is relevant
Book 3: Read all, ch 2 is where the Plot starts
Book 4: Read all, this is a big important chapter
Book 5:
Book 6:
Book 7:
Book 8:

VOLUME FOUR: Saint-Denis

Book 1:
Book 2:
Book 3:
Book 4:
Book 5:
Book 6:
Book 7:
Book 8:
Book 9:
Book 10:
Book 11:
Book 12:
Book 13:
Book 14:
Book 15:

VOLUME FIVE: JEAN VALJEAN
Book 1:
Book 2:
Book 3:
Book 4:
Book 5:
Book 6:
Book 7:
Book 8:
Book 9: