Hi my answer gonna work with any data, because some solutions in internet need primary key of rows, for my solution primary key is not required.
Here sample structure and sample dataset:
a b
1 23
1 23
16 59
12 12
13 45
12 12
45 56
Just group by all columns and add last column - count all (If there are more than two columns or more, you just need in "Aggregate" element put all columns and foreach set group by and in the end put "Count All" column):
Then just add conditional split element and take all rows where are more than 1 same row:
Real Example: