The climax of the play is the confrontation between Osembenga (and his men) and Mama Nadi (and her girls, including Salima, who dies at the end of the central conflict). The early conversation between Mama Nadi and Christian, during which she takes in Sophie and Salima to work for her, mostly provides exposition and background information that we need to understand the characters and context of the plot. The rising action begins when Jerome Kisembe, the rebel leader, visits Mama Nadi's, "hold[ing] court" with a crowd of rebel soldiers who hassle the girls. It is this action that Osembenga will later learn of and for which he will resent Mama Nadi, attacking and violating her girls unless she provides information about Kisembe's whereabouts. The rebel soldier who harasses Sophie, calling her a "bitch" and trying to force her to talk to him, is also part of the rising action. Likewise, Mama's conversation with Mr. Harari about her raw diamond is rising action as well as is the conversation between Sophie and Salima where Salima reveals her pregnancy.

I think it would be pretty easy to say that the climax of Ruined by Lynn Nottage is the dramatic death of the character Salima. So, rising action would be any action that takes place before that point in the play. Here are a few examples: 

1. In a scene that takes place during Christmastime, a drunken rebel soldier becomes rowdy inside Mama's bar. Mama has Salima dance with him in order to calm him down. 

2. Soon after Christian brings Mama the news that the Pastor has been murdered, a soldier named Fortune comes to Mama's looking for Salima. Here we learn that Fortune is Salima's husband, who failed to protect her and their child from rebels. 

3. When Osembenga comes to Mama's for the first time, Sophie tries to resist his aggressive advances, but Mama forces her to go off with him. 

All of these examples add to the trauma that the women forced to work for Mama experience and build up the tension that specifically leads to Salima's death.

One example is the arrival of Osembega at Mama's the first time.  At this point he is willing to unload his weapons and leave the ammunition at the door so that even if he gets upset, no one will get killed.  During his later visits, this will change, but this visit serves to heighten the tension and foreshadow later conflict in the establishment.

A second example is when Christian appears to announce that the white pastor, who was suspected of aiding the rebels, has been brutally murdered.  This demonstrates the rising danger to everyone around but also the lengths that Osembega is willing to go to to see revenge against those he perceives as his enemies.

A third example comes when Osembega arrives in Mama's for the second time and he demonstrates his desire to be with Sophie.  Her response of unwillingness and her demonstration of this by spitting on him drives the tension to new levels suggesting perhaps that the climax is soon to arrive.