Sagar,
I guess you are asking for something to start off with on a Pentax DSLR. A safe bet is an old manual lens for two reasons: Classic, slower speed lens designs often deliver smoother bokeh. And, old preset lenses have more aperture blades, which again is nice for smoother bokeh.
The easiest would be to have a look at the Helios 44M.... Goes for around 10,- US-dollars (let it be twenty) and has some nice old-school biotar bokeh.
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/29995-old-syle...4-2-bokeh.html
Here's some more suggestions regarding mainly macro bokeh,
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/31244-bokeh-ma...ggestions.html
Voe's 50 comparison, a real test:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/31897-comparin...us-lenses.html
Praise the Sonnar - another bokeh test:
Bokeh Test
Incredible: Jonas' thread asking for bokeh samples and here's the last listing of all lenses,
"Admirable" blur samples - FM Forums
If any of you have some photos to post here as examples, that'd be great!
The mole's vision: 55/1.2 on K100D (OK bokeh in my eyes)
All the best for next year, Georg (the other)