Other than brute force, are there any attacks on Threefish-512 using only a single known plaintext block? As per title, other than brute force, are there any attacks on Threefish-512 using only a single plaintext block? Are there any attacks like this in any other cipher?
According to Schneier,
there is an attack on 42 rounds of ThreeFish-512, but if you check out the analysis, it relies on multiple plaintext values. 

Wikipedia lists no singular known plaintext attack, only a boomerang attack, which also depends on multiple known plaintexts.

So given these sources, it would seem there is not a well known and effective attack on three fish 512 with only one plaintext block.

Generally speaking, given only an encryption of a single plaintext block it would be difficult to use cryptanalysis to break a cipher. Even block cipher modes of operation which are deprecated, such as ECB, will operate securely for single block-key encryptions. 

The Known-Plaintext-Attack seems to utilize single blocks of plaintext in some situations. That wiki site lists its usage on a cipher used during WWII, so technically Yes, there do exist ciphers which have been susceptible to a single known plaintext block at some points in history. But for modern ciphers, No, it does not seem to be an effective means of attack