在Angular 8中，可以在拦截器中订阅可观察对象，可以按照以下解决方案进行操作：

1. 首先，创建一个新的拦截器并实现HttpInterceptor接口：

import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable()
export class CustomInterceptor implements HttpInterceptor {
  intercept(req: HttpRequest, next: HttpHandler): Observable> {
    return next.handle(req).pipe(
      tap(event => {
        if (event instanceof HttpResponse) {
          // 处理响应数据
        }
      })
    );
  }
}

2. 在你的模块中，将此拦截器添加到提供者列表中：

import { NgModule } from '@angular/core';
import { HttpClientModule, HTTP_INTERCEPTORS } from '@angular/common/http';
import { CustomInterceptor } from './custom-interceptor';

@NgModule({
  imports: [HttpClientModule],
  providers: [
    {
      provide: HTTP_INTERCEPTORS,
      useClass: CustomInterceptor,
      multi: true
    }
  ]
})
export class AppModule { }

3. 现在，你可以在拦截器中订阅可观察对象。例如，你可以订阅请求的可观察对象：

import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable()
export class CustomInterceptor implements HttpInterceptor {
  intercept(req: HttpRequest, next: HttpHandler): Observable> {
    const modifiedReq = req.clone({ headers: req.headers.set('Authorization', 'Bearer your-token') });

    return next.handle(modifiedReq).pipe(
      tap(event => {
        if (event instanceof HttpResponse) {
          event.body = this.modifyResponseData(event.body);
        }
      })
    );
  }

  private modifyResponseData(data: any): any {
    // 修改响应数据
    return data;
  }
}

在这个示例中，我们修改了请求的头部，添加了一个授权令牌，并在收到响应后修改了响应数据。你可以根据自己的需求进行适当的修改。