What constellation does sun occupy by location and date? How can i find the location of the sun and which constellation it would occupy based on the location and date of year.

for example: an observer is in Des Moines, Iowa on April 10th, which constellation does the sun appear to occupy?
You can see for yourself for any date and location using the free Stellarium program (http://stellarium.org/).

The constellation that the Sun is in as seen from Earth does not depend noticeably on the precise location of the observer on Earth.  It depends mostly on the time of year.  Here are the approximate days of the year at which the Sun enters a new constellation:


Aries: April 18
Taurus: May 14
Gemini: June 21
Cancer: July 20
Leo: August 10
Virgo: September 16
Libra: October 31
Scorpius: November 23
Ophiuchus: November 29
Sagittarius: December 17
Capricornus: January 19
Aquarius: February 16
Pisces: March 12


The "approximate" part is that the Sun may be up to one day earlier or later than the quoted dates, just like the start of the seasons may be one day earlier or later than the average.  (Actually, it is the calendar that is early or late with respect to the phenomenon.)  Also, because of the precession of the equinoxes, these dates shift by about 1 day every 70 years.

See http://aa.quae.nl/en/antwoorden/sterrenbeelden.html#6.