I don't believe what you're asking exists, but I think more information is needed to fully understand your question.
Are you talking about a merge/inheritance feature?
What do you mean by "branch"? (I really, really hope it's not the old branched model technique!)
I'm looking at a file in branch A. I want to know if it was merged correctly to branch B. I know how to look at member history to find it out but I want to know if there is a command that can check.
I assume you are using change packages? If so, then through the GUI you could look for change packages that contain the member, and see which branches that member is part of.
I am not in the office now, but going by memory I believe the command you are looking for would be along the lines of si viewcp --fields=member,variant <Issue>:<ChangePackageID>.
For more information (such as other fields you would like want listed in your output), you can look at the command in detail by looking at the manpage for si viewcp on your local system, or look at the Integrity CLI Reference for Configuration Management.
I don't see an option in the si viewcp command that would tell me if a file is merged or not. The best it can show tell me is whether the file was propagated.
This shows up (as a dotted line) in the member history.
si rlog might show the information you are looking for. I haven't had a chance to test it yet.