I know a person isn’t supposed to bench with a medal knife on the the table.
Does this apply to על המחיה and בורא נפשות?
What if I’m at the table and I want to bench but others are still eating. so their knives are still on the table can I bench anyway with the knives on the table?
Interesting question. We do not have to hide the knife when saying anything else besides Birkat Hamazon. Eshel Avrohom O:CH 180-2 says that we only hide the knife if we are going to say the horachamon of… “v’al shulchan ze”. Another reason brought in the name of Salmas Chaim is that one of the reasons for covering the knife is because once a person was bentching and in middle of u’vnei he was so distraught that he took a knife and killed himself. Therefore we don’t keep a knife on the table because of that story. says Salmas Chaim that we are only careful during bentching since we are only careful for the exact story that happened, therefore it only applies to bentching and not anything else.
Regarding the knife, you do have to cover anything else but your knife, and not the knife of other people eating at the table. See Vaya’an Dovid 1- 28 (4).