How to search data with a 'knn query'?

[gengdeyin]

Please use the following questions as a guideline to help me answer
your issue/question without further inquiry. Thank you.

Which version of Elastic are you using?

[✔️] elastic.v7 (for Elasticsearch 7.x)
[ ] elastic.v6 (for Elasticsearch 6.x)
[ ] elastic.v5 (for Elasticsearch 5.x)
[ ] elastic.v3 (for Elasticsearch 2.x)
[ ] elastic.v2 (for Elasticsearch 1.x)

Please describe the expected behavior

How to search data with a 'knn query'?
just like the curl cmd:
curl --location 'http://{ip}:{port}/{vector_index}/_search?username=uanme&password=pwd'
--header 'Content-Type: application/json'
--data '{
"query": {
"knn": {
"vector": {
"vector": {vector},
"k": 2,
"ef": 100
}
}
},
"size": 10
}'

Please describe the actual behavior

Any steps to reproduce the behavior?