The most common and most likely answer to this crossword clue is the 11 letter word MIND-READER
I've seen this crossword clue in Financial Times
M
I
N
D
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R
E
A
D
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R
Buddy explains!
The straight part
We know that "Person to tell what you’re thinking" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case person to tell what you’re thinking = mind-reader.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 MIND-READER mean?
MIND-READER noun- A person with telepathic ability, capable of reading the thoughts of others around them.