What RNP level is required for an RNP approach if the chart does not specify a value?
RNP approaches require a minimum value of 0.30, be it LNAV only, LNAV/ VNAV or RNP AR. Most of the approaches around the globe are RNP approaches. So, they do not put in the value because it remains the same at 0.30.
In RNP AR approaches they put in the value because these are approaches that require specially trained pilots and specially equipped aircraft. That is where the AR comes from. It stands for Authorization required. The RNP AR approaches have RNP values starting from 0.30 down to 0.10. The biggest difference between a typical RNP approach and an RNP AR approach is the lateral obstacle clearance. In an RNP approach, you have a clearance of two times the RNP value (0.30 x 2 = 0.6 miles) and also a buffer of 0.2 miles either side. In an RNP AR approach, the buffer is taken out of the picture and it only offers two times the RNP number left or right. If the RNP value is 0.10, then the lateral obstacle clearance will be 0.20 miles either side. This allows tighter approaches in areas with high obstacles such as mountains (such as Innsbruck). But because such approaches are a bit demanding you need better equipment. So, airplanes that are not designed for it need extra modifications. These modifications will depend on the manufacturer and it will also depend on the actual procedure. The pilots who fly these approaches need extra training as well, so that they are more accustomed to flying it and to teach them the required contingency procedures. Depending on the operator and the aircraft configuration, an RNP AR approach maybe approved with an RNP value between 0.30 and down to 0.10. For example, Airbus offers A320 and A330 with modifications and approvals for either RNP AR approaches with 0.30 or 0.10. In case of the A350, the aircraft comes with RNP AR 0.10 approval as a basic setting.

For LPV approaches, there is not an RNP value as it is basically an ILS type approach flown to category I minima using the GPS and a ground based GPS signal augmentation system such as WAAS (Wide area augmentation system).