It's not unusual for inspectors to encounter evidence of a fire in an attic. Brown discoloration or light char is not a big deal. For severe fire damage you'll be passing along the structural evaluation to an engineer, but you'll impress clients if you can talk knowledgeably about this issue.

These articles explain why post-fire assessment of wood framing that is severely damaged requires a degree of expertise that few home inspectors have:

Post Fire Evaluation of Wood Framing (National Council of Structural Engineers Association)

Post-Fire Assessment of structural Wood Members (USDA)