implementing x(n+1) in digital circuit
As the comments suggest, if you want \$x(n+1)\$, you need to wait for it to arrive.  Of course, \$n\$ is arbitrary.  If you define time \$n\$ as ten samples ago, then you have available \$\{x(n+1), \ldots, x(n+9)\}\$.

If you want to predict (estimate) future values, you're asking a DSP question.  Linear prediction is a common approach for predicting future samples and is used in applications such as the audio coding (compression) used in the GSM cell phone standard.