"Q" is the obvious one. Without the "U", it is pronounced the same as "K". With the "U" it is pronounced as "Kw". "Queen" is easily replaced with "Kween".
The most useless letter could be "C", though. It makes the "k" or "s" sound. However, it is useful as "ch", and would be hard to replace with another letter.
We could however remove the "C" and replace it with the Russian letter "Ч" which is the "ch" sound in a single letter. The name of the letter is pronounced "cheh". "Cheese" would then be spelled "Чeese". It would take some getting used to, but it would simplify the language.
Another useless letter would be "x". It makes two sounds in English "ks" or "z".
There is absolutely no need for it in English. The only word which may be hard to change would be "x-ray". Even then, it could just be "eks-ray".
The letter E
E is the most frequently repeated letter in the English alphabet.
X
The letter E comes before the letter F in the English Alphabet and this is the case for most Alphabets that contain Latin Alphabet symbols that are derived from Greek.
q or x
the letter a
"E" is the most used letter in the alphabet followed by "T" as the second
a
The letter E
The letter E
E is the most frequently repeated letter in the English alphabet.
Q
X
Like most European languages, English is written in a modified Roman alphabet. The letter W is the most recent addition to it.
The letter E comes before the letter F in the English Alphabet and this is the case for most Alphabets that contain Latin Alphabet symbols that are derived from Greek.
q or x
C