If you have the userId or the username instead of the actors Id, you have to request the actorId via Webfinger.

http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e

In principle, profiles are public and anyone can read them. However, profiles are only created in rdf-pub when a logged-in user has submitted a request. So a profile can only be read after the user has made this request.
Get profile in turtle
curl --location --request GET 'http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e' \
--header 'Accept: text/turtle'
Turtle response
<http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e> a <https://www.w3.org/ns/activitystreams#Person>;
  <https://www.w3.org/ns/activitystreams#attributedTo> "http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4erdf-pub-server";
  <https://schema.org/identifier> "1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e";
  <https://schema.org/version> "1"^^<http://www.w3.org/2001/XMLSchema#long>;
  <https://www.w3.org/ns/activitystreams#Public> <http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4easPublic>;
  <https://www.w3.org/ns/activitystreams#inbox> <http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e/inbox>;
  <https://www.w3.org/ns/activitystreams#outbox> <http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e/outbox>;
  <https://www.w3.org/ns/activitystreams#preferredUsername> "fredy";
  <https://linkedopenactors.org/ns/rdfpub#outboxSparql> <http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e/outbox/sparql>;
  <https://linkedopenactors.org/ns/rdfpub#inboxSparql> <http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e/inbox/sparql> .
Get profile in json-ld
curl --location --request GET 'http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e' \
--header 'Accept: application/ld+json'----

.JsonLd response
[JsonLd response]
{
    "@graph": [
        {
            "@id": "http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e",
            "@type": [
                "https://www.w3.org/ns/activitystreams#Person"
            ],
            "https://linkedopenactors.org/ns/rdfpub#inboxSparql": [
                {
                    "@id": "http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e/inbox/sparql"
                }
            ],
            "https://linkedopenactors.org/ns/rdfpub#outboxSparql": [
                {
                    "@id": "http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e/outbox/sparql"
                }
            ],
            "https://schema.org/identifier": [
                {
                    "@value": "1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e"
                }
            ],
            "https://schema.org/version": [
                {
                    "@type": "http://www.w3.org/2001/XMLSchema#long",
                    "@value": "1"
                }
            ],
            "https://www.w3.org/ns/activitystreams#Public": [
                {
                    "@id": "http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4easPublic"
                }
            ],
            "https://www.w3.org/ns/activitystreams#attributedTo": [
                {
                    "@value": "http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4erdf-pub-server"
                }
            ],
            "https://www.w3.org/ns/activitystreams#inbox": [
                {
                    "@id": "http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e/inbox"
                }
            ],
            "https://www.w3.org/ns/activitystreams#outbox": [
                {
                    "@id": "http://localhost:8081/actor/1bdbbb62-3bb1-4a9c-8f7d-4a56e1696f4e/outbox"
                }
            ],
            "https://www.w3.org/ns/activitystreams#preferredUsername": [
                {
                    "@value": "fredy"
                }
            ]
        }
    ],
    "@id": "https://www.w3.org/ns/activitystreams#Public"
}