Hi Ashwin,
Depending on the issue at hand, the Project Charter, Communication Plan, HR Plan (Roles & Responsibilities), and Risk Management Plan are all areas where you might find escalation processes. First try and determine the type of problems that necessitate escalation and the Process Group the project is undergoing before answering a question of this magnitude.
The Project Charter is a good area to decipher escalation processes during Project Initiation because EEF & OPA can offer insight on organizational governance and organizational processes/standards. The Communications Plan will delineate parties that are authorized to receive information, those that need specific types of information, and the appropriate time to provide them with information. Therefore, escalations dealing specifically with communication are likely to be found in the Communication Plan, which is also organized early on in the project.
The Human Resources Plan offers guidance as to how resources are managed, controlled, and released under various circumstances. When resource constraints arise and issues or conflicts ensue as a result, the Human Resources Plan should help guide the team accordingly. Conflict Management is utilized as a tool and technique during the Manage Project Team process; therefore, the project manager should implement this technique when conflicts arise between team members. The successful execution of this technique will help facilitate optimal resolutions when team issues arise.
Finally, a thorough Risk Management Plan will contain options and actions to decrease project risks as they escalate. As the probability and impact of risks increase, it's vital to have thorough risk responses in place to reduce or alleviate the effects of escalating risks. I hope my explanation makes sense to you, as there are many different types of issues that can arise during a project. It's very important to understand what project phase and Knowledge Area you're dealing with before you can effectively escalate solutions and treat the problematic area(s) at hand. Please let me know if you need me to dive further into any of this.