"Is he big?"

[NRPL123]

veliky... is this the word to use in questions, instead of velky?

[BoneheadBass]

Both adjectives can mean "big" and generally they can be used interchangeably. And both can be be used in either a question or a statement.

[goldregenb]

I was given a mistake for using velky. Why?

[VladaFu]

Please always report the complete sentence. Your question cannot be answered. You can also use "My answer should be accepted".