Add a spiked end to timber
CC BY-SA 3.0 DontWorry

You could probably use any of


hand tools


hand axe and stump - and practice.
hand saw - and more practice, or a custom mitre-box/jig
drawknife
adze - and lots of practice
large chisels and mallet?

power tools


band saw
table saw with mitre-gauge or jig and clamps
chop-saw with jig for angle and external support for stake
sabre-saw (reciprocating saw)



For a one-off job I would use a hand saw to make four cuts to produce a point. If it came out off-centre I'd true it up with whatever hand tools I have to hand which worked best (maybe even a jack-plane set up for hogging off). Then keep practising.

I know you really are looking for a giant pencil sharpener

See also https://woodworking.stackexchange.com