How can I store latitude and longitude without PostGIS?
The simplest solution without PostGIS would be to store lat/long as two number columns.
numeric for exact precision.
double precision or even just real if you don't need the precision.

I see no reason why the data type point shouldn't work as well. Per documentation:


  Points are the fundamental two-dimensional building block for
  geometric types. Values of type point are specified using either of
  the following syntaxes:

( x , y )
  x , y

  
  where x and y are the respective coordinates, as floating-point
  numbers.


Related:


Which data type for latitude and longitude?