/usr/include/assa-3.5/assa/ is in libassa-3.5-5-dev 3.5.1-6build1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/assa-3.5/assa/Acceptor.h
/usr/include/assa-3.5/assa/Address.h
/usr/include/assa-3.5/assa/Assa.h
/usr/include/assa-3.5/assa/Assure.h
/usr/include/assa-3.5/assa/AutoPtr.h
/usr/include/assa-3.5/assa/CharInBuffer.h
/usr/include/assa-3.5/assa/CmdLineOpts.h
/usr/include/assa-3.5/assa/CommonUtils.h
/usr/include/assa-3.5/assa/ConUDPSocket.h
/usr/include/assa-3.5/assa/Connector.h
/usr/include/assa-3.5/assa/Destroyer.h
/usr/include/assa-3.5/assa/EventHandler.h
/usr/include/assa-3.5/assa/FdSet.h
/usr/include/assa-3.5/assa/FileLogger.h
/usr/include/assa-3.5/assa/Fork.h
/usr/include/assa-3.5/assa/GenServer.h
/usr/include/assa-3.5/assa/Handlers.h
/usr/include/assa-3.5/assa/INETAddress.h
/usr/include/assa-3.5/assa/IPv4Socket.h
/usr/include/assa-3.5/assa/IdSet.h
/usr/include/assa-3.5/assa/IniFile.h
/usr/include/assa-3.5/assa/LogMask.h
/usr/include/assa-3.5/assa/Logger.h
/usr/include/assa-3.5/assa/Logger_Impl.h
/usr/include/assa-3.5/assa/MaskSet.h
/usr/include/assa-3.5/assa/MemDump.h
/usr/include/assa-3.5/assa/PidFileLock.h
/usr/include/assa-3.5/assa/Pipe.h
/usr/include/assa-3.5/assa/PriorityQueue.h
/usr/include/assa-3.5/assa/PriorityQueue_Heap.h
/usr/include/assa-3.5/assa/PriorityQueue_Impl.h
/usr/include/assa-3.5/assa/PriorityQueue_STLPQ.h
/usr/include/assa-3.5/assa/Reactor.h
/usr/include/assa-3.5/assa/Regexp.h
/usr/include/assa-3.5/assa/RemoteLogger.h
/usr/include/assa-3.5/assa/Repository.h
/usr/include/assa-3.5/assa/Semaphore.h
/usr/include/assa-3.5/assa/ServiceHandler.h
/usr/include/assa-3.5/assa/SigAction.h
/usr/include/assa-3.5/assa/SigHandler.h
/usr/include/assa-3.5/assa/SigHandlers.h
/usr/include/assa-3.5/assa/SigHandlersList.h
/usr/include/assa-3.5/assa/SigSet.h
/usr/include/assa-3.5/assa/Singleton.h
/usr/include/assa-3.5/assa/Socket.h
/usr/include/assa-3.5/assa/Socketbuf.h
/usr/include/assa-3.5/assa/StdOutLogger.h
/usr/include/assa-3.5/assa/Streambuf.h
/usr/include/assa-3.5/assa/TimeVal.h
/usr/include/assa-3.5/assa/Timer.h
/usr/include/assa-3.5/assa/TimerCountdown.h
/usr/include/assa-3.5/assa/TimerQueue.h
/usr/include/assa-3.5/assa/UDPSocket.h
/usr/include/assa-3.5/assa/UNIXAddress.h
/usr/include/assa-3.5/assa/UnConUDPSocket.h
/usr/include/assa-3.5/assa/XDRHack.h
/usr/include/assa-3.5/assa/xdrIOBuffer.h