Like this

For more info go look up Shikimate pathway and Shikimic acid on Wikipedia.

Note that this is only one of the possible ways.

Usually many ways end up at L-tryptophane but the last step is the one that differs dmt containing from non dmt plants. :d

Of course all those reactions need energy because they need special enzymes and proteines. You(animals) and plants both use ATP for that. Plants can make ATP in different ways. We burn sugar and fats. Plant can use photosynthesis and the sugar made from photosynthesis to make ATP. Plants have mitochondria too that can burn sugar just like we do.