It's not unusual for inspectors to encounter evidence of a fire in an attic.
Determining residual load capacity requires more than visual examination. For fire damage assessment 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 requires a degree of expertise that few home inspectors have:
Post Fire Evaluation of Wood Framing (National Council of Structural Engineers Association)