I have seen big problems happen when people on a hike aren't evenly matched — when one is much stronger than the other, or has much more experience than the other. At the very least, it's good to know what each person's capabilities are, so you have appropriate expectations for the trip.
These are things to ask about a potential hiking partner:
- non-emergency situations
- What's your general fitness level?
- What's your physical fitness like regarding this specific activity? (hiking on slopes, scrambling, bicycling, XC skiing, carrying a heavy pack, etc)
- What's the longest hike you've taken?
- What's the most dangerous situation you've experienced on the trail, and how did you handle it?
- emergency situations
- Do you know the Ten Essentials?
- If I became incapacitated, could you:
- Use the GPS to navigate back and get help?
- Use the map and compass to navigate back and get help?
- Purify your water?
Have you trained in crevasse rescue?
Have you trained in using an avalanche beacon / probe / shovel?