Resolution:
Before EMS 4.4, you could use admin command "show stat consumers
topic=topic name" or "show stat consumers queue=queue name" to return
all the consumers on a topic/queue and their associated message
rate/second.  If you find a particular consumer is showing a
significantly lower value in rate/second columns than the others, then
it is a slow consumer candidate.
  
In the tibemsd.conf file, you can enable the rate_interval setting.  
rate_interval parameter sets the interval (in seconds) over which
statistics for routes, destinations, producers, and consumers are
averaged. By default, this parameter is set to 3 seconds.  Setting
this parameter to zero disables the average calculation.

=====================
tcp://localhost:7222> show stat consumers queue=queue.sample
                                            Total Count      Rate/Second
User            Conn  T  Destination        Msgs   Size      Msgs   Size
normalConsumer     9  Q  queue.sample      19411  872.0 Kb    537   24.2 Kb
slowConsumer      14  Q  queue.sample         13    0.6 Kb      1    0.1 Kb
=====================

E.g. in the above output, you could notice how normalConsumer rate and slowConsumer rate are differ.

After EMS 4.4, you can use "show consumers full", from the "Last Akcd"
value, you should able to narrow down the candidates.
  
Last Akcd  is the approximate time elapsed since last time any message
sent to the consumer was acknowledged by consumer's session. Value is
approximate with precision of 1 second.

Q: How can I detect slow consumer Candidates?