There is not a specified input resistance for the analog input and SPI lines provided in the datasheet because if will vary depending on your power supply voltage and current.
You can calculate the input resistance by measuring the input voltage and current on the line.
For Analog Input: VINA can reach up to VREF+ (VDD + 50mV) and IILA up to +/-1.5uA.
For example, if the measured values of VINA = 3.3V and IILA = 1.5uA, then input resistance to the analog input would be 2.2MΩ.
For Digital Input: VIH can reach up to (VOVDD x 0.75) and IIN up to +/-1.0uA.
For example, if VIH = 3V and IIN =1.0uA, then input resistance for the digital input would be 3MΩ.