mayqel qunenoS
>> If we want to say "I am there" we write {pa' jIHtaH}.

>> But if we want to say "I am not there", what do we write ?

>>

>>    {pa' jIHbe'} or {pa' jIHbe'taH} ?

Neither.  Write pa’ jIHtaHbe’ “I’m not there” which is a (neutral) statement of fact/location.  E.g.

  qepHomDaq jIHtaHbe'.  Saghal.
  [untranslated greeting from MO to qepHOM 2013]

I’ve never seen an example of [PRONOUN]be’taH.  If anything, pa’ jIHbe’taH might mean “I’m still not there” implying continuous absence over some time.

--
Voragh
Ca'Non Master of the Klingons