I have a taken the front wheel out of my motorcycle to replace the tyre. When I put the axle back in is it a good idea to grease it? If so what type of grease should I use?
I would apply a light coating of white lithium grease. It is thin enough that it it won't be wiped off the shaft sliding through the bearings. It also is resistant to getting washed off by rain or routine washing. The light coating of grease should keep the shaft from seizing in the bearings.
By all means yes. It is a good practice to grease the axle prior installation.