By Gram Slattery and James Oliphant SIOUX CITY, Iowa (Reuters) -A school shooting in Iowa, where Republican nominating contests begin next week for the U.S. presidential election, prompted prayers from among those wanting to be the party’s candidate, but elicited no substantial policy proposals among the top contenders. The incident saw a sixth-grade student killed and five people wounded after a 17-year-old opened fire on the first day of classes following the winter break, law enforcement officials said. Florida Governor Ron DeSantis, who is locked in a close battle for second in Iowa with f…