How to find modulo(%) of secp256k1 publick key ?

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I'm not completely sure what is "modulo(%)" of a public key, but my best guess is that you ask about the order of the points on the elliptic curve. It is returned by the method .order(). For secp256k1 it can be obtained as

p = ZZ('0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F')
E = EllipticCurve( GF(p), [0, 7] )
n = E.order()
print('decimal representation:', n)
print('hexadecimal representation:', n.hex())

This matches the curve parameters given on page 9 in Standards for an efficient cryptography.