Unclear point: how do we know gradient at time step $t+1$ in conjugate gradient descent$\,$?

Question

Below is the conjugate gradient descent algorithm. At time step $t$, how do we know gradient at time step $\;t+1\;,\;g(t+1)$, in the conjugate gradient descent ?

Reference: page 7-35, enter as password Paraskavedekatriaphobia : amlbook.com/eChapters/7-Jan2015-readeronly.pdf