"I do not like vegetables."
Translation:Jeg liker ikke grønnsaker.
When using object pronouns, the most neutral placement for the negation is after them. Placing the negation before the object pronoun is used for emphasis/comparison:
"Jeg liker dem ikke."
"I don't like them."
"Jeg liker ikke dem."
"I dont' like THEM."
"I don't like them (but I do like others)."
It's incorrect. That kind of construction is only used with object pronouns, and not with regular nouns (see my comment to donniecalico below).
If you want to use "ei" in this sentence, it's "Jeg liker ei grønnsaker.".
"Ei" and "ikke" are interchangeable when used as standalone words, but "ikke" can be used to form compounds whereas "ei" cannot. Either way, sticking with "ikke" is advisable unless you're aiming to imitate a dialect with a preference for "ei".