This snippet works in the specific situation where you have a boolean: it answers "how many non-Ns are there?".
SELECT LEN(REPLACE(col, 'N', ''))
If, in a different situation, you were actually trying to count the occurrences of a certain character (for example 'Y') in any given string, use this:
SELECT LEN(col) - LEN(REPLACE(col, 'Y', ''))
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