Hi Amer, you would have to do the experiment.

56Co and 58Co should have the same properties as 60Co, but are easier to obtain, have shorter half-lives and less deadly than 60Co.

 Many researchers have reported PB for effective removal of Cs but not for Co

Most probably it would be quite difficult. Cobalt forms a variety of rather stable chemical compounds with water, ammonia and chlorine, so it would be difficult to dislodge it from these compounds using Prussia blue. Different chemistry from the of of Caesium.

Yes! After chemical modification of the sorbent. Please read the paper by Chmielewska and Stachurska: J Radioanal Nucl Chem (2016) 307:1295–1301 DOI 10.1007/s10967-015-4291-2