Microflows in the process queue run in the system context and do not have a user specific context. Thus you cannot retrieve a session. However, if you need specific user information in that microflow, you can associate Account to QueuedAction, and retrieve Account in the microflow that is executed in the queue.
I will describe the detailed contents that I solved myself.
As Mr.Thorsten Biehl said, asynchronous Queues process run on the system, so there is no user session or information ($currentUser/$currentSession).
To that end, I thought of a way to pass user sessions and information to an asynchronous Queue process in advance using Java.
I customized the Queue handler (javasource/queue/usecases/QueueHandler.java).
1) Add Property:SessionId and UserName to Entity:Job of Domain Model of Queue.
2) After creating an asynchronous Queue process, set the session ID and user name ($currentSession/SessionId, $currentUser/Name) in Entity:Job.
3) Add as follows in the handler of asynchronous Queue process.
String sessionId = job.getSessionId();
String userName = job.getUserName();
IUser user = Core.getUser(context, userName);
ISession session = Core.initializeSession(user, sessionId);
HashMap<String, Object> jobInput = microflowRepository.getJobInput(jobObject, microflowName);
jobRepository.executeJob(context, microflowName, true, jobInput);
4) These sessions and user information can be passed to the asynchronous Queue microflow.
For example, we can set a context such as TeamCenter with this asynchronous Queue.
I thought about another method.
This is a method to start an asynchronous job in the main session without starting it in the system.
QueueHandler (IContext context_u, ILogNode logger,
this.context_u = context_u;
//context = queueRepository.getSystemContext(); // ← convert context from user context
context = context_u;