Explanation
The Cisco V-Edge Router performs QoS traffic classification on the ingress interface, before the traffic enters the VPN. The classification is based on the match criteria specified in the access lists, which can include the source and destination IP addresses, ports, protocols, DSCP values, and application-aware NBAR attributes.
The classification results in assigning a forwarding class and a QoS group to each packet. The forwarding class determines the output queue and the scheduling policy for the packet on the egress interface. The QoS group is an internal label that can be used to remark the DSCP value of the packet or to match the packet in another access list for further processing. References:
Forwarding and QoS Configuration Guide for vEdge Routers, Cisco SD-WAN Release 20, Chapter 2:
Configuring Localized Data Policy,
https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/qos/vEdge-20-x/qos-book/localized-da Cisco SD-WAN Design Guide, Release 20, Chapter 6: Quality of Service,
https://www.cisco.com/c/en/us/td/docs/solutions/CVD/SDWAN/2020/b_SD-WAN_Design_Guide_Aug_2

Explanation
According to the Cisco DNA Center Compatibility Matrix1, the current DNA-C 1.1 release supports the following wireless product families:
WLC 8540: This is a high-performance wireless controller that can support up to 6000 access points and
64,000 clients. It is designed for large-scale wireless deployments and offers advanced features such as application visibility and control, flexible radio assignment, and software-defined access2.
AP 3800: This is a high-performance access point that can support up to 5.2 Gbps data rates and 4x4 MIMO with four spatial streams. It is designed for high-density environments and offers features such as flexible radio assignment, CleanAir, ClientLink, and Smart Antenna Connector3.
WLC 3504: This is a compact wireless controller that can support up to 150 access points and 3000 clients. It is designed for small to medium-sized wireless deployments and offers features such as application visibility and control, software-defined access, and TrustSec4.
The other wireless product families, such as AP 1260 and WLC 5508, are not supported in the current DNA-C
1.1 release.
References:
1: Cisco DNA Center Compatibility Matrix
2: Cisco 8540 Wireless Controller Data Sheet - Cisco
3: Cisco Aironet 3800 Series Access Points Data Sheet - Cisco
4: Cisco 3504 Wireless Controller Data Sheet - Cisco

Explanation
A centralized SD-Access design is where a single fabric domain spans across the main site and all branch sites over the WAN. This design has some challenges, such as:
Since the traffic is encapsulated in VXLAN headers, SD-WAN features such as application-aware routing, QoS, and security policies cannot be applied to the traffic based on the original IP headers. This means that the SD-WAN controller cannot optimize or route the traffic based on the application or user identity. The traffic is treated as a single class of service across the WAN.
The centralized design also introduces a single point of failure and a potential bottleneck at the main site, where the border nodes and the control plane nodes are located. If the main site goes down or the WAN link fails, the branch sites will lose connectivity to the fabric domain and the external networks.
The centralized design also requires a high bandwidth and low latency WAN connection between the main site and the branch sites, which may not be feasible or cost-effective for some scenarios.
References :=
Some possible references are:
Cisco Enterprise Networks SDA, SDWAN and ISE Exam for System Engineers (ENSDENG) Study Guide Cisco SD-Access and SD-WAN Integration Design Guide