Atomic spectroscopy or gravimetric analysis.
A well-equipped lab would put a solution through an atomic spectroscope (AA, ICP, DCP) for a quick determination of the metal component.
A "wet chemical" gravimetric method would be to precipitate the metal as another salt (a phosphate, for example), then weigh the resultant mass. Sufficient sample quantity and careful labwork will give you a different final mass for the two different compounds.
Generally, all potassium salts (K) are soluble, so even a hydroxide or phosphate precipitate in solution would qualitatively identify strontium if it is an either/or question.
Strontium Phosphate insolubility
General solubility rules