。
Have you informed your parents about your plan?
Literal
Parents [to-に] your plan [object-を] informed [resultative-てありますか]?
~てある is the resultative state of a transitive verb: 知らせてある means 'the informing has been done and the result persists' — they've been told and now know. Different from ~ている, which focuses on the ongoing action or state; ~てある emphasizes the completed result of a deliberate action.