Do we say shir ha Malos when benching birchat hamazon on Pesach Sheini?
The rule is that we say Shir Hamaa’los before bentching on days that we don’t say tachanun. There are different opinions and inhagim if tachanun shouldbe said on Pesach Sheini or not. therefore saying Shir Hama’alos will depend on what your minhag regarding tachanun is.
Sharei Teshuva O:CH 131-19, Aruch Hashulchan 170-1, Sharei habracha 1-35 ftnt. 67.