I just tested doing a GET request via a HTTP Request Node sending data via the query-parameters with spaces.
Did send them to:
and
Both times it did display the URLs with %20 and the actual value with spaces. So all seems to work corectly.
Here the output from webhook.site:
The node did look like this:
Anyway, if you really have to encode it manually for some reason you can use the encodeURI function. So if your current expression looks like this:
{{ $json["name"] }}
you would change it to:
{{ encodeURI($json["name"]) }}