Knowledge is a key asset in software engineering. Facilitating access to the knowledge that software engineers require for the task at hand can therefore bring many benefits. To accomplish this, it is important to understand how knowledge flows through the organization, to identify problems that may hinder a suitable flow, and to define strategies with which to address them. Process modeling has proved to be a useful technique for analyzing knowledge flows. Traditional process modeling languages do not, however, provide primitives to explicitly represent the knowledge involved in the processes within the models. In this paper, we illustrate how the Software Process Engineering Metamodel (SPEM) can be adapted, to be used as a process modeling language for analyzing knowledge flows in software processes. We have extended SPEM to represent knowledge and its sources in process models in an explicit way. We also discuss the experiences obtained from using this extension in a software organization and the lesson we have learned from it.